单选题 ______ is often the case with a new idea, much initial activity and optimistic discussion produce no concrete proposal.
A. It B. Which C. As D. That

【正确答案】 C

【答案解析】本题测试as引导非限定性定语从句的用法。as作为连词，代替后面整个句子，意为“正像，正如”。