since引导的时间状语从句。主句和从句的时态用什么？

Sb. has done sth. since sth. happened. 自从某事发生以来，某人做了某事 Sb. has been doing sth. since sth. happened.自从某事发生以来，某一直在做某事 这是 since的句型 since引导的时间状语从句中，要用过去时，表示“自从过去某个时间以来” 其主句用现在完成时或现在完成进行时（强调动作的持续性）。 He has learned five songs since he came here. 自从他来这儿以来，已