—  Why didn't you chat with that friendly foreigner just now?

—  I'd like to, but the trouble was ___ ___ he said was difficult for me to understand. [ ]

A. what which    

B. that what        

C. that that    

D. what that

如图所示，理想变压器原副线圈匝数比为n₁∶n₂=4∶1，原线圈回路中的电阻A与副线圈回路中的负载电阻B的阻值相等.a、b端加一恒定交流电压后，两电阻消耗功率之比P_A∶P_B=________，两电阻端电压之比U_A∶U_B=________.