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17. "cannot…too…"结构,"cannot…too…"意为"It is impossible to overdo…"或者，即"无论怎样……也不算过分"。"not"可换用"hardly"，"scarcely"等，"too"可换用"enough"，"sufficient"等
You cannot be too careful.
18. "否定+but "结构，在否定词后面的"but"，具有"which not"，"who not"，"that not"，等等否定意义，构成前后的双重否定。可译成"没有……不是"或"……都……"等
Nothing is so bad but it might have been worse.
19. "否定+until (till)"结构，在否定词"no"，"not"，"never"，"little"，"few"，"seldom"等的后边所接用的"until/till"，多数情况下译为"直到……才……"，"要……才……"，把否定译为肯定。
Nobody knows what he can do till he has tried.
20. "not so…but"和"not such a …but"结构，这两个结构和"否定+but"的结构差不多，不同之点是这两个结构中的"but"是含有"that…not"意味的连续词，表示程度。可译为"还没有到不能做……的程度"，"并不是……不……"，"无论怎样……也不是不能……"等。
He is not so sick but he can come to school.
21. "疑问词+should…but "结构，这个结构表示过去的意外的事，意为"none…but"，可译为"除了……还有谁会……"，"岂料"，"想不到……竟是……"等。
Who should write it but himself?
22. "who knows but (that)…"和"who could should…but"结构，这个结构是反问形式，一般意译为"多半"，"亦未可知"等等，有时也可直译。
Who knows but (that) he may go?
23. "祈使句+and"和"祈使句+or"结构，"祈使句+and"表示"If…you…"，"祈使名+or"表示"if…not…，you。
Add love to a house and you have a home. Aad righteousness to a city and you have a community. Aad truth to a pile of red brick and you have a school.
24. "名词+and"结构，在这个结构中，名词等于状语从句，或表示条件，或表示时间
