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.

[Q]: Which statement best compares single-celled and multi-celled organisms?  
 (A) Tissues in a single-celled organism are like the cells in a multi-celled organism. (B) The nucleus in a single-celled organism is like the skin of a multi-celled organism. (C) Organelles in a single-celled organism are like the organs in a multi-celled organism. (D) The cytoplasm in a single-celled organism is like the nervous system in a multi-celled organism.
[A]: C


[Q]: How much time is required for a bicycle to travel a distance of 100 m at an average speed of 2 m/s?  
 (A) 0.02 s (B) 50 s (C) 100 s (D) 200 s
[A]: B


[Q]: When making observations in nature, what is the best way for students to show respect for the environment?  
 (A) Stay on the paths. (B) Not take samples. (C) Take photographs. (D) Leave the area exactly as they found it.
[A]:
D