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.

The nucleus of the cell controls cell activity. Which body system performs a similar function in humans?  
 (A) circulatory system (B) central nervous system (C) skeletal system (D) integumentary system
B

A tropical rain forest contains many tall trees. Smaller plants with large leaves grow at the base of the tall trees. The large leaves are most likely an adaptation of the plant due to which condition?  
 (A) lack of sunlight (B) lack of oxygen (C) lack of water (D) lack of food
A

An octopus has special cells in its skin called chromatophores which enable the octopus to change its color almost instantly. The chromatophores most likely help the octopus  
 (A) swim faster. (B) breathe slower. (C) hide from predators. (D) regulate body temperature.

C