单选题 For an advertisement to be effective, its production and placement must to be based on a knowledge of human nature and a skilled use of the media.

【正确答案】 C

【答案解析】答案：C 分析：助动词must后面应该跟直接动词原形，而不用添加介词to。改正：to be based → be based 翻译参考：为了使一个广告更加有效，它的制作和策划必须建立在对人类本性的了解以及对媒体的熟练运用上。