Be quick.__you'll miss the early bus

D
= If you aren't quick,you'll miss the early bus
or= otherwise; or else 否则
如果是肯定意味,用and
如：
Use your head,and you'll find a way.
开动脑筋想想,你会找到办法的
= If you use your head,you'll find a way.
不懂追问*^__^*