[rú guǒ]
if; in case; in the event of; supposing that
Were this to happen ...
如果这样
If it hadn't been for him, we would have gone astray.
如果不是他的话，我们就迷路了。
In case she comes, let me know.
如果她来的话，告诉我一声。
If it were not for the vapour in the air, there would be no dew.
如果空气中没有水气，就没有露水。
If necessary, we can use aluminium instead of steel.
如果必要，我们可用铝代钢。
We can't keep abreast of the developing situation unless we study harder.
我们如果不加强学习， 就会跟不上形势。
The object of these experiments was to find the connection, if any, between the two phenomena.
这些实验的目的就是探索这两种现象之间的联系，如果存在着任何联系的话。
In the event (that) our team wins, there will be a celebration.
如果我队获胜， 我们将庆祝一番。
In the event of fire, ring the alarm bell.
如果着火， 就按警铃。