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 Input:
Which of the following is most likely to disrupt the natural balance in an ecosystem?  
 (A) introduction of a non-native species (B) reduced daylight hours during winter (C) preventing the cutting of trees in forests (D) riverbank erosion resulting from springtime flooding

Ex Output:
A


Ex Input:
Earth is composed of layers of material with different properties. Which of the following is most likely to be in constant motion?  
 (A) core (B) mantle (C) oceanic crust (D) continental crust

Ex Output:
B


Ex Input:
An artificial pacemaker is a device that regulates the beat of the heart by an electrical stimulus. Some early pacemakers were powered by batteries and were worn externally with wires passing through the skin to the surface of the heart. Modern pacemakers are now much smaller and are implanted surgically. Which most likely has increased the lifespan and effectiveness of artificial pacemakers?  
 (A) the development of thinner wires (B) the invention of lithium batteries (C) mass production of pacemaker parts (D) reducing the cost of producing pacemakers

Ex Output:

B