32．___________the many ways illegal immigrants come into the United States every year, the vehicle crammed with crowds seems to be the method of choice lately, however, tragedies such as deaths on the journey to the destination, are sometimes reported nowadays．

下列四个实验中只需要完成三个就可以证明Fe、Cu、Ag三种金属的活动性顺序。其中不必进行的是（）

若定义在R上的函数f(x)满足$f\left(1-x\right)=f\left(x+3\right)$,且$\left(x-2\right)f^{\text{'}}\left(x\right)$<0,a="f" (${\log }_{2}5$),b="f" (${\log }_{4}15$),c="f" ($2^{0.5}$)，则a,b,c的大小关系为(        )

北宋兴起的景德镇，后来发展成为著名的（　　）

下列光学器件中，能对光线起发散作用的是（    ）