3.定义集合A∗B={z∣z=xyA*B=\{z\vert z=xyA∗B={z∣z=xy,x∈Ax\in Ax∈A,y∈B}y\in B\}y∈B},设集合A={−1A=\{-1A={−1,0,1}1\}1},B={−1B=\{-1B={−1,1,3}3\}3},则A∗BA*BA∗B中元素的个数为((( )))