关于necessary.it is necessary to do sth.it is nec关于necessary. it is necessary to do sth. it is necessary to doing sth. 两者有什么区别?什么时候用to do .什么时候用 to doing?请回答,
问题描述：
关于necessary.it is necessary to do sth.it is nec
关于necessary. it is necessary to do sth. it is necessary to doing sth. 两者有什么区别?什么时候用to do .什么时候用 to doing?请回答,
答