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.

Which of these activities is used to conserve water?  
 (A) planting crops that survive in droughts (B) running water while brushing teeth (C) washing vehicles frequently (D) watering grass after a rainfall
A

Which of these do all cells release?  
 (A) sugar (B) water (C) energy (D) oxygen
C

The Late Heavy Bombardment was a period of extensive comet impact on Earth about 3.8 billion years ago. Scientists believe this period provided much of the matter now found in which part of the Earth system?  
 (A) core (B) mantle (C) atmosphere (D) hydrosphere

D