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.

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.
C

A student makes the hypothesis that rubbing a balloon on a shirt and then putting it on the wall will cause it to stick due to static electricity. Once the experiment is conducted, what is the best way to prove that the results are reliable?  
 (A) Write down the results of the experiment. (B) Repeat the same experiment several times. (C) Make another hypothesis about static electricity. (D) Conduct a different static electricity experiment.
B

A student is given three identically sized blocks. Each block is made of a different material. What characteristic of the blocks should be examined to find out which block is made of metal?  
 (A) color (B) weight (C) texture (D) conductivity

D