TASK DEFINITION: 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.
PROBLEM: Robert is a fisherman who wants to find a way to catch more fish. He decided to try different sizes of hooks. Robert caught 4 catfish, 3 trout, and 7 perch while using worms for bait. Which is the independent (manipulated) variable in Robert's investigation?  
 (A) type of bait (B) size of hook (C) type of fish caught (D) number of fish caught

SOLUTION: B

PROBLEM: A potential negative impact of building a dam on a river is that the dam   
 (A) prevents sediment from flowing downstream. (B) increases the amount of water available to farms. (C) prevents seasonal downstream flooding. (D) increases the rate of water loss from a lake.

SOLUTION: A

PROBLEM: A turtle eating worms is an example of  
 (A) breathing (B) reproducing (C) eliminating waste (D) taking in nutrients

SOLUTION:
D