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.

Q: Students are designing kites to discover what type of kite flies the highest. Which is the most important to consider when designing a kite to fly high?  
 (A) string length (B) surface area (C) materials used (D) time of day

A: B
****
Q: Which example best shows structures that make up the digestive system in the human body?  
 (A) heart, blood, vessels (B) nose, trachea, lungs (C) brain, spinal cord, nerves (D) esophagus, stomach, intestines

A: D
****
Q: In order to locate a beetle population, scientists must use a highly specialized piece of equipment. Which factor would most likely limit the ability to locate beetles?  
 (A) climate (B) expense (C) sample size (D) politics

A:
B
****