since eithe when because tostop problems surf shestudiedhard but
4 lunchisready let sstop lunch tohave 3 hestudiedhard the
如: 1. if they had studied hard, they could do it easily now.
(3) since 过去时的从句 he has studied hard since he came to
引导结果状语从句 so… that… i studied so hard that i got the