Correct answer: A. By deep colours or isobaths
Explanation: The direct answer is option A: very deep parts of the ocean floor can be shown with deeper colours or isobaths. First understand the idea. A map cannot normally show depth by looking at the actual bottom, so it uses symbols. A bathymetric map represents underwater relief. Different shades of blue or other depth colours can show increasing depth. Isobaths are lines joining places that have equal depth, just as contour lines join places of equal height on land. Option A is correct because both deep colours and isobaths are accepted methods. Option B, flower pictures, gives no measurement of ocean depth and is decorative rather than geographical evidence. Option C, counting trees, is unsuitable because trees do not measure underwater depth. Option D, sunlight amount, may affect the sea surface or climate but does not directly indicate the depth of the floor. Thus A is the only relevant scientific answer. Exam cue: contours show equal height on land, while isobaths show equal depth under water.