四格表χ2检验的检验假设是（）
A.P1=P2
B.P1≠P2
C.π1=π2
D.π1≠π2
E.P≠兀
参考答案：C
It is reported that great efforts made to ________ the case have paid off.[ ]
A. run into
B. look into
C. run after
D. look after
“蓝牙”技术指的是一种无线通信技术。
