适当形式填空
100

As more children were born,more food ______(need).

was needed

200
Later,they learned to work with the _______(season),

planting at the right time and,in dry areas,________(make)use of annual floods to irrigate their fields.

seasons,making

300

Agriculture gave people their first experience of the power of technology________(change) lives.

to change
400

This aging of the population is driven_______two factors.

by


500

The population becomes________(old) than before.This is __________(particular) true in the US.

older,particularly
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