unit 3 computer知识点讲解
原创人：北大附中河南分校王萍
1.i began as a calculating machine in france in1642.
translate：__________________________________________________
现在分词作定语可以表示修饰词的性质，特征。现在分词通常表示主动意思
translate: excitingnews________arunning man__________
thetrain leaving at ten_______ ___
fallingleaves_______fallenleaves_________
a surprising look____________ asurprised look___________
连接高考：
1 the _____ look on her face suggested that she______ itbefore.
a surprising; wouldn’tknowb suprising; hadn’t know
c surprising; hadn’tknowd surprised; shouldn’t know
2 a communicative satellite______ as much as 3.5 tons was sentup into space last week.
awighingb weighed cto beweighedd being weighed
3 scientists have______ that the world’s population will doubleby the end of this century.
a numbered bincludedccalculatedd designed
2.i developed very slowly and it took nearly two hundred yearsbefore i was built as an analytical machine by charlesbabbage.
before用于这类句型的结构有：
it didn’t take/was long before------过了不久就-----
it will take/ be longbefore------要过很久----
it won’t take/be long before------不久-----
translate：
it didn’t take long before the fire was under control
it will be five years before we meet again
选学：
① this / it is the first / second…time +that 从句。that从句一般用现在完成时，如果把前边的is改为was，则that从句用过去完成时。如：
this is the first time i have come here.
it was the third time (that) he had made the same mistake.
② it is / has been +一段时间 + since从句。since从句中用过去完成时。
it was ten years since we had had such a wonderful time.
③ be about todo…when…意为“即将……（这时）突然……”。如：
i was about to go out when the telephone rang.
④ be (was /were) + doing… when…意为“正在干……（这时）突然……”。
they were reading when tom shouted in pain.
⑤ hardly had…done…when… ; no soonerhad…done…than…
when 和than从句里用一般过去时，表示“刚刚……就……”。如：
hardly (no sooner) had i got home when (than) the rain poureddown.
