Mapping of the ocean floor

Correct answer: B. Bathymetry

Explanation: Bathymetry deals with measuring depths of seas and lakes. Exam tip: understand a bathymetric map as a depth map.

Correct answer: C. Sound wave

Explanation: The correct answer is option C, sound wave. Modern sea-depth measurement commonly uses echo sounding or sonar, in which a sound pulse is transmitted toward the seabed and the returning echo is detected. If the speed of sound in the water is known or suitably estimated, depth can be calculated from depth = speed × travel time ÷ 2, because the measured time covers the downward and upward journeys. Light is strongly absorbed and scattered in seawater, heat waves are not a depth-measuring method, and ordinary radio waves do not travel effectively through deep seawater. Thus sound is the suitable wave.

Correct answer: D. Sea floor

Explanation: The sound wave strikes the sea floor and returns. Exam tip: depth is found from the travel time.

Correct answer: A. Bathymetric map

Explanation: A bathymetric map shows ocean depth and relief. Exam tip: think of it as the oceanic form of a topographic map.

Correct answer: B. Shallow submerged part near a continent

Explanation: The continental shelf is the shallow sea area near the coast. Exam tip: connect it with fisheries and mineral resources.

Correct answer: C. It forms a steep slope from shelf to deep ocean

Explanation: The continental slope connects the shallow shelf with deep ocean basins. Exam tip: remember slope comes after shelf.

Correct answer: D. Broad nearly flat plain in the deep sea

Explanation: An abyssal plain is a broad and flat area in the deep ocean. Exam tip: count it among the flattest oceanic features.

Correct answer: B. Long narrow and very deep depression

Explanation: Oceanic trenches are among the deepest parts of the sea floor. Exam tip: connect trenches with subduction zones.

Correct answer: C. To find depth and shape using sound waves

Explanation: Sonar uses sound waves to show distance and shape of the sea floor. Exam tip: study sonar with echo sounding.

Correct answer: D. Seamount

Explanation: A seamount rises from the sea floor but often does not reach the surface. Exam tip: connect it with volcanic origin.

Correct answer: A. Guyot

Explanation: A guyot is a flat-topped seamount. Exam tip: remember the difference between guyot and seamount.

Correct answer: B. Ocean floor relief

Explanation: Colours and shading help understand ocean depth and shape. Exam tip: remember the role of blue shades in showing depth.

Correct answer: C. Isobath

Explanation: Isobaths join points of equal ocean depth. Exam tip: contours are for land and isobaths are for sea depth.

Correct answer: D. Travel time of sound

Explanation: The time taken by the sound wave to return helps find depth. Exam tip: remember the relation of time and sound speed.

Correct answer: A. Oceanography

Explanation: Oceanography studies ocean depth and floor features. Exam tip: connect ocean mapping with geography and oceanography.

Correct answer: B. It shows mid-oceanic ridges and trenches

Explanation: Ridges and trenches are linked with plate boundaries. Exam tip: connect ocean features with plate movements.

Correct answer: C. In continental shelf and slope areas

Explanation: A submarine canyon is a deep cut valley on the sea floor. Exam tip: remember it as a valley-like ocean feature.

Correct answer: D. Broad deep area of the ocean floor

Explanation: An oceanic basin is a large deep part of the ocean floor. Exam tip: connect it with abyssal plains and deep-sea features.

Correct answer: A. Deep sea was difficult to observe and measure directly

Explanation: The direct answer is option A. Earlier, complete knowledge of the ocean floor was limited because the deep sea was difficult to reach, observe and measure directly. Step by step: sunlight becomes weak with depth, pressure increases greatly, and ordinary ships cannot see the bottom. Scientists therefore needed special instruments, sound waves, underwater vehicles and later sonar mapping to estimate depth and shape. Option A correctly identifies the main difficulty. Option B is false because oceans have always contained water; the problem was studying their hidden floor, not the absence of water. Option C is false and irrelevant: ships were necessary for exploration, although ordinary ships alone were not enough for deep measurement. Option D is false because oceans are real physical water bodies, not objects existing only on maps. Modern technology gradually improved measurements and made detailed bathymetric maps possible. Exam cue: limited earlier knowledge means difficult access and measurement, not a non-existent ocean.

Correct answer: B. It can measure depths over a wider area at once

Explanation: A multibeam system uses many sound beams to show detailed relief. Exam tip: connect it with detailed mapping.

Correct answer: C. To estimate floor relief from small sea-surface height changes

Explanation: Satellites help estimate large floor features from sea-surface variations. Exam tip: understand satellite mapping as an indirect method.

Correct answer: D. It directly measures depth by sound at the location

Explanation: Ship-based survey measures depth at specific locations. Exam tip: connect it with sonar survey.

Correct answer: A. Coastal geological structure differs from place to place

Explanation: Coastal structure and geological history affect shelf width. Exam tip: remember that shelf width is uneven.

Correct answer: A. It helps ships choose safer routes

Explanation: Knowledge of depth and obstacles supports safe navigation. Exam tip: remember the practical use of mapping.

Correct answer: B. It helps identify possible mineral and energy areas

Explanation: Relief information makes resource areas easier to identify. Exam tip: remember the link between shelf and mineral zones.