本文已收藏至：英語資料積累
need ＂不必做＂和＂本不該做＂
表示因果推理關(guān)系的連詞：主要有so, for, then, therefore等舞骆。
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届腐，because酒奶，as，since在用法和意義上的區(qū)別：
1 for引導(dǎo)的句子是并列分句免绿，只能后置郭脂，并用逗號與前面的句子隔開。主要用來表示推測性原因嘶伟，或附帶解釋、說明前一分句的情況又碌。
如The electric current must have been turned off, for the light went out.
2 because用來引導(dǎo)表示直接原因的從句九昧，語氣很強，明確地說明因果關(guān)系毕匀。其引導(dǎo)的從句可置于句首铸鹰、句末或句中。如He is absent today because he is ill.
for引導(dǎo)分句表示因果關(guān)系時皂岔，它可以和because互換使用蹋笼。
如上句也可以說成：He is asent today, for he is ill.
但表示推測性原因，就不能互換使用躁垛。如He must be ill, for he is absent today.
3 since剖毯，as都是不講自明的原因，是已知的原因教馆，as的語氣比since要弱逊谋。
如Since (As) you don't feel well, you had better stay at home.
