China is _____vast country which is home to _____amazing variety of landscapes,plants and animals.   [ ]

A. the;the      

B. a;the      

C. the;an        

D. a;an

电磁式直流测速发电机，为了减小温度引起其输出电压的误差，可以在其励磁绕组中串联一个比励磁绕组电阻大几倍而温度系数大的电阻