instruction:
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.
question:
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
answer:
B


question:
An astronomer is studying two stars that are the same distance from Earth. Star X appears brighter than star Y. Which statement best explains this observation?  
 (A) Star X is larger than star Y. (B) Star Y is larger than star X. (C) Star X reflects the Sun’s light better than star Y. (D) Star Y reflects the Sun’s light better than star X.
answer:
A


question:
The Periodic Table of the Elements is arranged so that elements with similar characteristics are in the same column. Which element is a highly reactive metal?  
 (A) chlorine (Cl) (B) helium (He) (C) magnesium (Mg) (D) silver (Ag)
answer:

C