16. When you visit a foreign country, it is important to know how to ask for help politely.

（教材原句英语翻译句子练习，考查It’s + adj. + to do sth.“做某事是...”的运用英语翻译句子练习；know后面使用“疑问词+ to do”英语翻译句子练习；短语ask (sb.) for help“(向某人)寻求帮助”；polite作形容词，“礼貌的”；反义词: impolite；副词：politely）

17. It is not enough to just ask a question correctly. We also need to learn how to be more polite.

（教材原句，考查句型：“It is not enough to do sth.”表示“做...的不够的”；correct作形容词“正确的”；也可作动词“纠正”correct mistakes“纠正错误”；第二句中learn后接疑问词+to do，依然是宾语从句与简单句的转换形式；此句中省略how也可以，构成learn to do sth. “学习/学会做...”）

18. The proper expressions depend on whom they are speaking to or how well they know each other.

（教材原句，考查宾语从句的运用，此句中whom与how引导的宾语从句做动词短语depend on“依靠，取决于”的宾语；whom表示“谁”，是who的宾格形式，常作宾语，此句中作speak to的宾语；know sb.“知道/了解某人”；each other = one another“相互，彼此”；expression“表达，表情”）