1、as…as,the same as. 否定句用not so\as…as,not the same as

从句中常用省略句: eg:He runs as fast as he can.

2、as if, as though (虚拟语气)

1、as,just as “如…”“正如…一样”Do just as you like

5、providing,provided that, suppsing,suppose (that),given (that) “如果，只要，假如”

4、in case既可引导目的状，又可引导条件状=”if it happened that…”

3、so\as long as,on condition that “条件是…”“只要..”

2、unless. 反面条件=if not　 主句为否定意味，从句为肯定句(从句也可用否定结构)

　 unless做介词 “除非，如果不”

1、if正面条件“如果”

4、such that (是这样…以致)

3、such…that　

such…that(状从)

　　 such…as(定从)