The volunteers will visit the primary school next Monday ,_______all the students are children of migrant workers,

A．which

B．who

C．when

D．where

下列现象中属于全球变暖对我国带来的影响有

A．森林带向北移

B．造成生物多样性的增加

C．南方沙尘暴现象明显增多

D．北方地区农业生产结构改变