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.

Ex Input:
What characteristic of DNA results in cell differentiation in developing embryos?  
 (A) which genes are present (B) how many copies of each gene are present (C) which genes are active (D) what protein is produced by a gene

Ex Output:
C


Ex Input:
Scientists have measured the rate of growth of the Atlantic Ocean basin to be about 2 to 3 cm per year. This type of activity coincides with the formation of ridges on the ocean floor. What is the most likely cause of this activity?  
 (A) erosion from tidal action (B) the deposition of sediment (C) the flow of continental basalt (D) movement from tectonic plates

Ex Output:
D


Ex Input:
Gregor Mendel's observation of pea plants is an example of  
 (A) research-based evidence supporting a scientific theory. (B) a conclusion being tested by a hypothesis. (C) random testing during an experiment. (D) evidence for and against a scientific model.

Ex Output:

A