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]: Which characteristic of frogs is an adaptation to living in water?  
 (A) strong legs (B) webbed feet (C) dull colors (D) moist skin
[A]: B


[Q]: A scientist uses angstrom units to measure the distance between two points. The scientist is most likely measuring the distance between two  
 (A) atoms. (B) cities. (C) continents. (D) stars.
[A]: A


[Q]: A dietary supplement manufacturer developed a new calcium supplement that appears to increase the bone density in middle-aged women. When tested in a small clinical trial, the supplement was shown to cause a 15% increase in bone density in 8 out of 10 women. Before the supplement is offered to the general public, which step should the manufacturer take next?  
 (A) add a variety of vitamins to the supplement (B) test the supplement on mice in the laboratory (C) develop packaging that is attractive to women (D) test the supplement on a larger sample of women
[A]:
D