6.______ carefully,Michael!There's a school ahead.( )
A. | Drive | B. | To drive | C. | Drove | D. | Driving |
5.It is the first time since last summer we_______ each other.( )
A. | have met | B. | met | C. | had met | D. | will met |
4.My old father began to study computer at the age of sixty______ he might keep up with times.( )
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A. | if | B. | so that | C. | although | D. | unless |