初二完形填空Scientists are trying to make the deserts（沙漠） into goo

初二完形填空
Scientists are trying to make the deserts（沙漠） into good land again.They want to bring water to the deserts,so people can live and grow food.They are ___1_____ a lot about the deserts.But more and more of the earth is becoming desert all the time.Scientists may not be able to change the desert in time.
Why is more and more land becoming desert Scientists think that people make deserts.People are doing bad things to the earth ,for example,they often cut trees down,build houses in the fields .
Some places on the earth don’t get very much rain.But they still don’t become deserts.This is because some green plants are growing there.Small green plants and grass are very important to dry places.Plants don’t let the hot sun make the earth even drier.Plants don’t let the wind blow the dirt away.When a little bit of rain falls,the plants hold the water.Without plants,the land can become a desert much more easily.
1 A learning B making C doing D living
附加理由,