Given the task definition and input, reply with output. 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.

Scientists have been able to insert genes from a spider into the genome of a domestic goat. When the goat matures, it produces milk that contains a protein found in spider webs. This protein can then be extracted and used to make strong but lightweight materials for bulletproof vests, automobiles, and aircraft. The change does not cause the goat any pain, but some people think that it is not right to add genes from the genome of one animal to another. Which word best describes this concern?  
 (A) economic (B) biological (C) ethical (D) practical

C