①当a<0时,函数y=f(x)有零点;
②若函数y=f(x)有零点,则a<0;
③存在a>0,函数y=f(x)有唯一的零点;
④若函数y=f(x)有唯一的零点,则a≤1.
①他很后悔没有接受街坊的劝告。____、____
②他急忙跑到田里。____
There are three _______ assistants in the _______ shop.