建议/命令/要求
一些表示建议/命令/要求的动词后面所接的从句要使用动词原形表示虚拟语气
1. 表建议: advocate主张, advise, move, recommend, suggest, propose
2. 表命令: order, decree颁布/命令/裁决, mandate命令/指令/要求, command命令/控制, demand
3. 表要求: request, require, insist, require of sb. that
但是，allow/rule后面不需要这样使用
allow/ permit/ forbid/ prohibit 后面不引导宾语从句
allow/ permit/ forbid + sth
+ sb to do
prohibit sb from doing
only if
只有当(只是在 ... 的时候)
例句:
Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学。
I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款，我才买得起那栋房子。
A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题，只有当所有子句为真时，该句才为真
