第二节 完型填空 阅读下面短文，从短文后所给的[A]、[B]、[C]三个选项中选择能填入相应空白处的最佳选项。 In some countries, there is very【16】rain at any time. The farmers there【17】irrigate (灌溉) their fields. Irrigation is【18】if there is a big river【19】the crops, and【20】there is plenty of water in it. Canals (沟渠)【21】the river water to the fields when necessary. In some seasons【22】may be too much water in the river, and the【23】may flood all the land near the river.【24】other times the river water may not be enough for all the farmers, and then it will be【25】to irrigate the fields. (16)