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]: To calculate the relative age of rocks, geologists use the rate of radioactive decay of isotopes present in their samples. What is the term used for the original amount of the elemental isotopes being investigated?
(A) rare earth isotopes (B) son isotopes (C) daughter isotopes (D) parent isotopes
[A]: D

[Q]: Which occurs as a result of Earth's tilt on its rotating axis?
(A) movement of the tides (B) prevalent or trade winds (C) seasonal changes in the climate (D) light and dark changes of day and night
[A]: C

[Q]: Which environmental problem was directly caused by the invention of the automobile?
(A) storage of nuclear waste (B) increase in air pollution (C) increased use of pesticides (D) flooding in the Midwest
[A]:
B