1) We should learn all the new words by heart in order to ........ our vocabulary. (rich)2) The rotation of crops on the same land can prevent soil ............ (exhaust)
3) Our farms produce rice, crops, and dairy ...... (produce)
4) We must make ......... for our old age by saving money. (provide)
5) The industrial ......... will lead to the country's prosperity. (develop)
6) Some large cities have had measures to minimize air ........ (pollute)
7) The ................ of the swamps will destroy the mosquitoes' breeding places. (drain)