Only when you stay and live with___ local people for a period of time will you have    

____better understanding of life here.

A．a;/

B．the;a

C．/;the

D．the;the

把一个底面半径6厘米，高3.6厘米的圆锥形铁制零件，改铸成底面半径为3厘米的圆柱形零件，铸成的圆柱形零件的高是多少厘米？