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:
Growth and activities of organisms can speed up the chemical weathering of rocks. Which organisms naturally cause most of the chemical weathering of rocks?
(A) small mammals (B) plant seedlings (C) mosses (D) insects
answer:
C

question:
Tobias rode his bike on a road for a 2 hr period. On average, he passed a 1 km marker every 3 min during this period. Which of the following was his average speed for this 2 hr period?
(A) 10 km/hr (B) 15 km/hr (C) 20 km/hr (D) 25 km/hr
answer:
C

question:
Many people get fresh water from wells that reach water stored underground. When there is little rain, the water can begin to run out. Which step is best to make the water last longer?
(A) using sprinklers for fewer hours each week (B) washing vehicles in the middle of the day (C) spraying water to clean oil from parking lots (D) letting faucets run while brushing teeth
answer:
A