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.

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.
D

A biological community is made up of all the  
 (A) populations living in an area (B) natural resources present in an area (C) members of a species on Earth (D) environments on Earth
A

The electromagnetic spectrum is the complete range of electromagnetic radiation ranging from radio waves to gamma rays. Which type of radiation in this spectrum is associated with observable colors such as red, green, and blue?  
 (A) gamma rays (B) X-rays (C) visible light (D) radio waves

C