1.因为killed the dog是过去动作,在我问他之前,"他已经这样做了",因此要用现在完成时he has done so.
2.I am sure+that从句,是一个固定结构,再:在that从句中__he said 是一个句子来做主语,叫主语从句,这个主语从句缺少宾语,因此要用what.因此选D that what.
注:be sure of/about 后不能跟一个完整的句子,只能跟宾从作介宾.如:I am sure of/about what he said .是正确的.
而I am sure of /about what he said is true.就是错误的.
3.be afraid +that从句,这是一固定结构.只有that才能引导从句,介词是不能引导从句的.
4.选A that not all things can be done.
that引导的叫同位语从句,说明得出了什么结论.
because只能引导原因状语从句
5.that是用来引导表语从句,且不能省略that .当主语为"...原因"(the reason/why...)时,表从用that引导,而不能用because引导,因为because只能引导原因状语从句.