instruction:
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.
question:
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.
answer:
B


question:
A dragonfly develops through incomplete metamorphosis. Which stages does the dragonfly's life cycle include?  
 (A) egg and larva (B) egg and nymph (C) larva and pupa (D) larva and nymph
answer:
B


question:
Which tool would be best for students to use to observe and measure plant cells?  
 (A) microscope (B) hand lens (C) metric ruler (D) triple-beam balance
answer:

A