under 后接某些名词可以用表示被动意义，表示“在被……的过程中”，under cultivation 的意思是“在被开恳中”（=being cultivated）。

Some extra land is being brought under cultivation in Asia. 在亚洲有些额外的土地正在被开恳。

又如：

The hotel is still under construction. 旅馆还在兴建中。

The matter is under investigation. 此事正在调查中。

All categories of expenditure are under review. 各项开支正在审查中。

Four new power stations are currently under construction. 四座新的发电站目前正在建设中。

The port was coming under attack from enemy warships. 那个港口正遭到敌人战舰的攻击。

The possibility of employing more staff is still under discussion. 招聘更多员工的可能性仍在讨论中。