69. We are talking about if this plan should be carried out. If 和whether都可以引导动词的宾语从句,如果从句做的是介词宾语,只能用whether引导。所以把if 改为whether。
70. I can not decide if to stay or not. 只有whether才能和不定式搭配使用。因此把if 改为whether。
71. My suggestion is we try for a second time. 表语从句的引导词如为that,一般不省略。因此在we前加上that。
72. What will the professor say is not known yet. 名词性从句的语序都是陈述句语序。因此应改为:What the professor will say is not known yet.
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