converting cropland to forestland and grassland的用法和样例：
例句
- The program of the converting farmland into forest is a big systems engineering,which involes broad converage, invests much money and has high participation of farmers.
退耕还林是一项庞大的系统工程，覆盖面广，投资多，农民参与程度高。 - The rate of converting arable land into forestland is relatively lower compared with grassland.
还林的比例相对还草较低，目前的还林结构主要是未成林造林地。
