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1. Leonard: Sheldon, just let it go. Sheldon，别纠结了，让它过去吧！
Sheldon：if I could, I would, but I can’t, so I shan’t. 如果我可以的话，我会的，但是我不可以，所以我不会。
解析：
If：如果；是否；假如；要是
（1）表示条件：主句将来时，if从句用现在时表示将来
例：I will arrive on time if you invite me to the party tomorrow.
如果明天的聚会你邀请我的话，我将准时到达。
What is to become lf me if you go away?
如果你要走的话，我的结果会是怎么样？（这里to become不定式表示将来）
（2）表示是否
例：I wonder if you agree with my opinion.
不知你是否同意我的观点
（3）表示虚拟：意为假如。
a.与现在事实相反
主句：should（would或could）+动词原形 从句：一般过去时
例：if I were you, I would not talk to him now.
如果我是你，我不会现在去和他说话。
If there were not for the water vapor in the air, there would be no dew.
如果空气中没有水汽，就没有露水。
b.与过去事实相反
主句：should（would或could）+动词原形 从句：过去完成时had +动词过去分词
例：if you had studied harder at that time, you would have entered a better university.
如果你那时候好好学习的话，你能考上更好的大学。(过去没有好好学习)
If the second world war had not happened, the economics of USA had not been so advanced.
如果二战没有发生过，美国的经济不会如此发达。.
c.对将来的假设
主句：should（would或could）+动词原形 从句：were+动词不定式或should+动词原形
例：if you were to make up your mind, everything would not be difficult.
如果你下定决心，任何事都不会困难。
拓展1：if only与only if
If only：要是，如if only i were you ；而only if：只有……才，如only if you work hard, can you get promoted.(主句倒装)
拓展2: shan’t, shall not的缩写；Shall 用于第一人称表示征求意见。
2．Sheldon：But……since that’s what it looks like, we can rule that out. 但是，因为“不是看起来的那样”，我们可以排除那种情况。
解析：
rule：n.规则，统治；v.统治，规则
rule out：排除，排斥；不考虑；划去
例：The Treasury Department has ruled out using a weak dollar as the main solution for the country's trade problems.
财政部已经不考虑使用疲软美元作为解决该国贸易问题的主要办法。
The disaster ruled her out a permanent future for the ballerina in dancing.
那场灾难使这个芭蕾舞女演员永远无法跳舞了。
Rule it out：排除可能性
例：The police man thought the most possibility of homicide, but Joe held the view that the woman died from the commit suicide and didn’t rule it out.
警察认为这个女人死于他杀，但是Joe觉得不排除自杀的可能性。
拓展：rule-out排除法
3. Sheldon: Although what I lack in leadership, apparently I more than make up for in sewing. 虽然我没什么领导能力，不过我的锋刃技术还不错。
解析：
make up for：弥补，补偿
例：I just want to make up for my faults before.
我只是想弥补我之前的过错。
What she lacks in ability makes up for in circumspection.
她的细心弥补了她能力上的不足。
拓展：make up组成，构成；编造；化妆