Scientists didn’t know much about lung cancer _____.1.before long 2.until recently 3.long before 4.in the past few years

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Scientistsdidn’tknowmuchaboutlungcancer_____.1.beforelong2.untilrecently3.longbefore4.inthepastfewye

Scientists didn’t know much about lung cancer _____.1.before long 2.until recently 3.long before 4.in the past few years
Scientists didn’t know much about lung cancer _____.
1.before long
2.until recently
3.long before
4.in the past few years

Scientists didn’t know much about lung cancer _____.1.before long 2.until recently 3.long before 4.in the past few years
3 long before

4 Scientists didn’t know much about lung cancer in the past few years
在过去的几年里科学家们并不知道太多关于肺癌的事
didn't是过去时态 因此从句也要用相应的过去时态

3 long before