You are given a science question (easy-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]: Which of the following best describes an advantage of using a mass production manufacturing system instead of a custom manufacturing system?  
 (A) Customers can provide specific feedback to workers. (B) Workers become skilled in all aspects of assembly. (C) Goods can be easily modified for customers. (D) Products can be made at a lower cost.
[A]: D


[Q]: A scientific guess about the cause and effect of an event is called  
 (A) a variable. (B) a theory. (C) a hypothesis. (D) an observation.
[A]: C


[Q]: Natural processes cause rapid and slow changes to Earth's surface. Which event causes changes to Earth's surface most rapidly?  
 (A) an earthquake shaking the ground (B) sediment washing into a bay (C) a rainstorm weathering rock (D) water flowing in stream
[A]:
A