You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

[Q]: Why are some rocks smoother and rounder than others?  
 (A) They have the shapes of the minerals from which they are made. (B) They were smoothed by the action of wind and water. (C) They were squeezed up through the soil. (D) They hardened in rounded pockets of soil.
[A]: B


[Q]: What is a main feature of plains?  
 (A) a flat, level surface (B) a high, steep peak (C) a low, shallow basin (D) a gentle, gradual slope
[A]: A


[Q]: The transfer of thermal energy from one object to another is known as  
 (A) heat. (B) electricity. (C) magnetism. (D) temperature.
[A]:
A