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]: Organisms contribute to the water cycle mainly through the process of  
 (A) irrigation. (B) evaporation. (C) precipitation. (D) transpiration.
[EX A]: D

[EX Q]: Which part of an atom is involved in chemical reactions?  
 (A) nucleus and its particles (B) negatively-charged particles (C) neutrally-charged particles (D) positively-charged particles
[EX A]: B

[EX Q]: A single prokaryotic cell can divide several times in an hour. Few eukaryotic cells can divide as quickly. Which of the following statements best explains this difference?  
 (A) Eukaryotic cells are smaller than prokaryotic cells. (B) Eukaryotic cells have less DNA than prokaryotic cells. (C) Eukaryotic cells have more cell walls than prokaryotic cells. (D) Eukaryotic cells are more structurally complex than prokaryotic cells.
[EX A]:
D