—The problem isn't difficult for the children to work out, is it？

—_____ . Perhaps they should have been given a more difficult one. 

A．Yes, it is

B．Yes, it isn't

C．No, it is

D．No, it isn't

膝关节三联征是指

A．外侧副韧带、内侧半月板及前交叉韧带损伤

B．内侧副韧带、外侧半月板及前交叉韧带损伤

C．内侧副韧带、内侧半月板及前交叉韧带损伤

D．外侧副韧带、内侧半月板及后交叉韧带损伤

E．内侧副韧带、内侧半月板及后交叉韧带损伤