(单选题)

The tech industry expo, which attracted more than 180,000 people, was a reminder of ______ the industry is best at: being optimistic about itself.

A.that

B.how

C.what

D.which

参考答案：C

参考解析：

考查what引导的宾语从句。句意：吸引了18万余人参加的科技产业博览会提醒人们，科技产业最擅长的是对自己保持乐观。介词of后面是宾语从句，从句没有引导词，且从句中缺少宾语，所以用what起双重作用，故选C。

知识点：