You are given a science question (hard-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.

A student plans to design a new toothpaste tube that will give the same amount of toothpaste every time it is squeezed. Which should the student do first when designing the new tube?
(A) make a data table of amounts of toothpaste (B) gather building materials (C) create models of old toothpaste tubes (D) draw a few possible solutions
D

Dr. Tanaka discovered a new virus. The virus has a single strand of a nucleic acid, but she does not know if it is DNA or RNA. After running tests, she concludes that it is DNA. Which of the following would lead her to that conclusion?
(A) It contains uracil. (B) It contains adenine. (C) It contains thymine. (D) It contains cytosine.
C

Dumping toxic chemicals into a pond would most likely result in
(A) an increase in oxygen levels in the pond. (B) plants near the pond growing more quickly. (C) the toxic chemicals having no effect on the pond. (D) fish in the pond being harmed or dying off.
D