—I don't know _____ during the summer vacation. Any advice?
—How about doing some part-time jobs?
本题考查宾语从句的用法。宾语从句要用陈述句语序，先排除 A 和 B；根据答语“做一些兼职工作怎么样？”可推断，我不知道暑假期间“我应该做什么”，故答案为 C。
—Has Mike received his mother's mail?
—Yes,he signed for it _____ this morning.
句意：——迈克已经收到他母亲的邮件了吗？——是的，今天早上他亲自签收的。in person 亲自；in fact 实际上；in silence 沉默地。由句意可知答案为 A。
—What's the meaning of "The Belt and Road"?
—Let me _____ the words in the new dictionary.
本题考查 look 短语的含义。根据本题语境可知，让我在新词典里查阅一下这些单词，故 look up 符合题意。