I don't have to introduce him to you__you know the boy A until B unless C since D but

I don't have to introduce him to you__you know the boy A until B unless C since D but
I don't have to introduce him to you__you know the boy A until B unless C since D but

I don't have to introduce him to you__you know the boy A until B unless C since D but
选 C
since 既然
既然你知道这个男孩,我就没有必要向你介绍他了.

C
既然你认识这个男孩，我就不用先你介绍他了。

since
在这里表示因为，我不必解释他，因为你知道这个男孩