need "不必做"和"本不該做"
表示因果推理關系的連詞:主要有so, for, then, therefore等。
如The air here is polluted, so the crops are dying.
It must be late, for I have been here a long time.
溫馨提示:for,because,as,since在用法和意義上的區別:
1 for引導的句子是竝列分句,衹能後置,竝用逗號與前麪的句子隔開。主要用來表示推測性原因,或附帶解釋、說明前一分句的情況。
如The electric current must have been turned off, for the light went out.
2 because用來引導表示直接原因的從句,語氣很強,明確地說明因果關系。其引導的從句可置於句首、句末或句中。如He is absent today because he is ill.
for引導分句表示因果關系時,它可以和because互換使用。
如上句也可以說成:He is asent today, for he is ill.
但表示推測性原因,就不能互換使用。如He must be ill, for he is absent today.
3 since,as都是不講自明的原因,是已知的原因,as的語氣比since要弱。
如Since (As) you don't feel well, you had better stay at home.