"明天如果下雨，我就待在家"写成 If it will rain tomorrow, I will stay home，老师就圈了。这就是"主将从现"的坑。
常见连词分组
时间：when 当……时，while 正当，before/after 在前后，until 直到，as soon as 一……就
- I'll call you when I arrive.
条件：if 如果，unless 除非
- If it rains, we cancel the picnic.
原因：because 因为，since 既然
- I stayed home because I was sick.
让步：though / although 虽然
- Though he is young, he knows a lot.
主将从现（重点）
主句将来时（will / be going to），when / if / as soon as / until 引导的从句用一般现在时，不能用 will：
- 错：If it will rain, I will stay.
- 对：If it rains, I will stay.
- 对：When he comes, I'll tell him.
主从句位置可换
从句放前面加逗号，放后面不加：
- If it rains, I'll stay. / I'll stay if it rains.
口诀：时间条件主将从现，从句现在别用 will；原因让步随便放，前面从句加个逗。
