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.

[EX 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.
[EX A]: B

[EX Q]: If 1 kg of the compound toluene melts at -95°C, then 500 g of toluene will  
 (A) melt at -47.5°C. (B) melt at -95°C. (C) boil at 95°C. (D) boil at 47.5°C.
[EX A]: B

[EX Q]: Teresa is making a list of the similarities and differences between a euglena and a volvox cell. In which way is the euglena different from the volvox cell?  
 (A) A euglena can respond to light. (B) A euglena can live in fresh water. (C) A euglena can regulate water intake. (D) A euglena can only reproduce asexually.
[EX A]:
D