Scientists have to work hard to keep _____ with modern discoveries and developments. [ ]

What beautiful shoes you’re wearing! Theymust be expensive. —No. they only10yuan.

I shall never forget those years _____ I lived on the farm with the farmers,____ has a great effecton my life [ ]

Bob is taking the desks away because they ______ too much room.

_______ is the population of your hometown, Lucy—It’s about 15,000.