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]: In which case does a physical change occur?  
 (A) Ice melts into water. (B) Bread burns in a toaster. (C) A cake bakes in an oven. (D) Two chemicals form a new substance.
[EX A]: A

[EX Q]: Some scientists believe that the mass extinction of dinosaurs was caused by the impact of a large meteorite on Earth. This impact would have caused a darkening of the sky due to dust blown into the upper atmosphere. This darkening would have reduced the sizes of some ecosystems because of  
 (A) longer seasons. (B) accelerated erosion. (C) reduced photosynthesis. (D) increased number of hurricanes.
[EX A]: C

[EX Q]: Three scientists conducted the same experiment to analyze the effectiveness of a cleaning agent on household bacteria. What is the main advantage of having the experiment repeated?  
 (A) More bacteria will be destroyed. (B) The results will be more reliable. (C) A scientific journal will publish their work. (D) The conclusion will lead to new discoveries.
[EX A]:
B