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.

In the human body, which system functions primarily to defend the body against disease?  
 (A) digestive (B) immune (C) nervous (D) respiratory
B

A hardware designer finds that the wiring in a circuit is releasing enough heat to make the circuit dangerously hot. Which change would best solve this problem?  
 (A) increasing the current in the circuit (B) placing rubber insulation on wires in the circuit (C) reversing the direction of current flow in the circuit (D) using circuit wires with a lower resistance
D

Natural processes shape the surface of Earth. Most canyons are formed by ___.  
 (A) ice (B) plants (C) steady winds (D) moving water

D