Star formation, formation of planets, and our solar system

Correct answer: C. Stars give energy by fusion and planets generally reflect light

Stars produce their own light while planets reflect light. Exam tip: identify both by energy source.

Correct answer: D. The Sun and planets formed from a rotating gas dust nebula

Nebular theory considers the solar system to have originated from a common rotating cloud. Exam tip: remember it as the main idea of solar system origin.

Correct answer: A. In massive outer protoplanets

Massive outer protoplanets could attract light gases more strongly. Exam tip: connect gas accretion with the large mass of outer planets.

Correct answer: A. A dense carbon dioxide atmosphere

The governing concept is the greenhouse effect: a planet’s atmosphere allows incoming solar energy to enter but absorbs and re-emits outgoing infrared radiation, trapping heat near the surface. Venus has an exceptionally dense atmosphere composed mainly of carbon dioxide, a strong greenhouse gas. Its thick clouds and atmospheric pressure reinforce the heat-trapping process, producing extremely high surface temperatures. Option A is correct because the dense carbon dioxide atmosphere is the major cause. Option B would prevent atmospheric heat trapping, option C is inconsistent with Venus’s hot surface, and option D is false because Venus is relatively close to the Sun. The question belongs to planetary formation and the solar system because it compares planetary conditions.

Correct answer: A. Because water and fine sediment accumulate behind natural levees

Correct answer: A. Natural levees rise beside a river channel during floods. Beyond them, floodwater moves slowly and can become trapped, allowing fine sediment to settle in a low-lying area with poor drainage. This area is called a backswamp. The other options describe glacial, coastal, and wind processes.