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.

Five bowling balls are lined up touching one another on a smooth surface. Striking the first ball with a hammer makes the fifth ball move away from the group. The force of the hammer was transmitted through the line of balls as what type of wave?  
 (A) electromagnetic (B) heat (C) longitudinal (D) transverse
C

How does a parachute sufficiently increase air resistance to allow the parachutist to land safely?   
 (A) by decreasing the force of gravity acting on the parachutist (B) by decreasing the total mass of the parachutist (C) by increasing the surrounding air pressure around the parachute (D) by increasing the total surface area of the parachute
D

Which statement explains why most salmon leave salt water and return to fresh water?      
 (A) It is a learned behavior that maintains the population. (B) It is a learned behavior that maintains salt concentrations. (C) It is an inherited behavior that maintains the population. (D) It is an inherited behavior that maintains salt concentrations.

C