说一件可能发生的事，用 if + 一般现在时，然后用 will + 动词：If the bus is late, I'll walk.
If + 一般现在时，然后用 will
If the bus is late, I'll walk.
If you call me, I'll come.
Not "If the bus will be late, I'll walk." — say "If the bus is late, I'll walk.". if 后面用一般现在时，不用 will。
试一试: Woman: Our team is playing tonight. Man: If they ___, we'll have a party. 选出那个男人会说的话。 (lose / will win / win / will lose) 答案: win — 赢了才开派对，所以是 if they win；if 后面用一般现在时，不用 will。
if 从句放在后面
if 从句可以放在后面，跟在主句后。这时不加逗号：I'll call you if I see her.
I'll call you if I see her.
She'll be angry if you forget.
试一试: Woman: I don't have an umbrella. Man: You'll get wet if it ___. 选出那个男人会说的话。 (stops / rains / will stop / will rain) 答案: rains — 下雨会把人淋湿，所以他说 if it rains；if 后面用一般现在时，不用 will rain。
If you don't …, you'll …：如果你不……，你就会……
用 If you don't … 说会发生什么不好的事：If you don't hurry, you'll be late.
If you don't hurry, you'll be late.
If you don't study, you won't pass the test.
试一试: Man: I'm going to bed at two in the morning. Woman: If you ___ sleep more, you'll be tired tomorrow. 选出那位女士会说的话。 (do / don't / will) 答案: don't — 凌晨两点太晚了，所以她说：if you don't sleep more, you will be tired.
每次都这样：两次都用一般现在时
说 every time（每次）都会发生的事，两个分句都可以用一般现在时：If you are cold, you put on a coat.
If you are cold, you put on a coat.
If I eat late, I don't sleep well.
试一试: Woman: Why do you take the bus to work? Man: If I ___ there, I can't find a place to park. 选出那个男人会说的话。 (walk / will drive / drive / will walk) 答案: drive — 开车就要找地方停车，每次都这样，所以是 if I drive；if 后面用一般现在时。