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]: Researchers are developing new types of crop plants with desirable characteristics such as disease resistance and drought tolerance. Crossing plants so that the next generation will express desirable traits is best described as  
 (A) selective breeding. (B) natural selection. (C) genetic engineering. (D) gene sequencing.
[EX A]: A

[EX Q]: Which land feature is formed from erosion by waves?   
 (A) a sandbar (B) a sea cliff (C) a barrier reef (D) a barrier island
[EX A]: B

[EX Q]: What role does the centromere play in cellular reproduction?  
 (A) It is the area where microtubules are formed. (B) It is the area where the nucleus is during cell division. (C) It is the area of alignment for the chromosomes. (D) It is the area of attachment for chromatids.
[EX A]:
D