条件从句通常可由下列词或短语来引导：
as long as　supposing (that)　if
so long as　on condition that　unless
suppose (that)　providing / provided (that)
例句
a. If it rains tomorrow, I will take my umbrella. （条件从句中要用一般现在时表示将来）
b. Don’t worry about the mistakes you may make in conversation,so long as you can make yourself understood in English.
c. I may lend you the book on condition that you return it to me in time.
d. I will agree to go provided that my expenses are paid.
只要有人替我付钱，我就同意去。
e. Suppose flights are fully booked on that day—which other day could we go?
假定那天的航班都订满了——我们还可以在哪天走呢？