1 calm down and you will find a way out 这是祈使句,calm用原形,when in face of danger 作时间状语,但省略下东西.还原后是 when you are in face of danger ,you caml down and you will find a way out.
2前半句是完全倒装,后面强调了out ,放后也行,体现不了出来.
3选B that[引导的是同位语从句,解释命令的具体内容]; should leave[是过去将来时]
4 选 D What[主语从句]-- What -is hard
5 选 C What we call the Theory of Relativity 问题是对主语提问,回答是选择主语从句