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]: Which unit is used to indicate the amount of energy in food?  
 (A) ounce (B) degree (C) calorie (D) gram
[EX A]: C

[EX Q]: A large number of species on Earth became extinct during a short time period about 65 million years ago. Based on this pattern of extinction, which is the most likely cause?  
 (A) gradual climate change (B) continued climate stability (C) sudden global climate change (D) gradual ecosystem succession
[EX A]: C

[EX Q]: During a walk through the Arkansas River Valley, Alex found a rock that she determined was a sedimentary rock. Which characteristics of the rock would lead Alex to this conclusion?  
 (A) thin flaky sheets and very hard (B) glassy texture and a shiny black color (C) very rough texture with obvious crystals (D) sand-sized particles and a light brown color
[EX A]:
D