My sister still wanted to go to school bue she was

My sister still wanted to go to school bue she was

我妹妹（姐姐）想去上学,但她生病了.

我姐姐仍然想去上学， 但是她病了。

虽然我妹妹病了但仍然想去上学。

我妹妹（姐姐）想去上学，但她生病了。
绝对正确
老师讲了。。。。
句中不是bue是but