题目

T appreciate that it's not easy for you, but you ______ try to get here on time． A．may          B．must          C．will       D．can 答案：B实轴长是2a的双曲线，其焦点为F1，F2，过F1作直线交双曲线同一支于A、B两点，若|AB|=m，则△ABF2的周长是A.4aB.4a-mC.4a+2mD.4a-2m