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]: A student hypothesizes that algae are producers. Which question will best help the student determine if this is correct?  
 (A) Do algae consume other organisms? (B) Which organisms consume algae? (C) Do algae use sunlight to make food? (D) Could an ecosystem survive without algae?
[EX A]: C

[EX Q]: A student examines a new watch design. The watch has a small solar cell on its face. The main function of the solar cell is to  
 (A) reduce the cost of the watch. (B) provide an energy source for the watch. (C) make the watch more attractive. (D) stop the watch from speeding up.
[EX A]: B

[EX Q]: A student uses a telescope to view stars at night. The student notices some of the stars are different colors. The color of a star is determined most by its  
 (A) size. (B) distance from Earth. (C) mass. (D) temperature.
[EX A]:
D