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]: All of the following can become fossils except  
 (A) bones. (B) shells. (C) teeth. (D) rocks.
[A]: D


[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]: An organism, such as a nematode worm, may have only 1000 cells. It should be classified as being  
 (A) a virus. (B) a bacteria. (C) unicellular. (D) multicellular.
[A]:
D