英语中的“虽然……但是，though， but”，“因为……所以，beacuse， so”等关联词不能连用，只能用其中的一个连词。因为though， because是从属连词，引导复合句；but， so是并列连词，引导并列句。一个句子不可能既是并列句又是复合句，所以though， but不能连用，beacuse， so不能连用。
例句：
1、Though he is young， he knows much knowledge.
He is ； young， but he knows much knowledge.
2、Because Mary was ill， she was absent from school.
或者：
Mary ； was ill， so she was absent from school.
