He's still unable to make himself____in English.为什么要填understood而不是understand?

He's still unable to make himself____in English.为什么要填understood而不是understand?
因为make sb done意思是：“使某人【被】做”.make himself understood意思是：“使他自己被别人理解”.
make sb do sth 意思是：“使某人做某事”.
如：The boss made them work day and night.老板使他们日夜干活.