We have been good friends ( )we joined the same ping-pang te

选C呢.自从我们加入同一乒乓球队,我们就成了好朋友（现在仍然是）.
1、如果用after应该用过去时这么来说：
We became good friends after we joined the same ping-pang team.
after是基于当时的时间之后的一段时间说的,所以是过去时.
2、而since常基于现在,言外之意是from that time up till now
3、用until或者before
We didn't know each other until (before) we joined the same ping-pang team.