语法总结
真实条件句
If 从句用一般现在时，主句可用 will、情态动词或祈使句：If you park..., a policeman will find it.
相似句：
- If it rains, I will take an umbrella.
- If you see him, tell him to wait.
fail to do 与 cannot fail to do
fail to do 表示“未能做”，cannot fail to do 在本课语境中表示“一定会做”。
相似句：
- He failed to obey the rule.
- You cannot fail to notice the sign.