下列说法不正确的是

A．三个角的度数之比为1∶3∶4的三角形是直角三角形

B．三个角的度数之比为3∶4∶5的三角形是直角三角形

C．三边长度之比为3∶4∶5的三角形是直角三角形

D．三边长度之比为5∶12∶13的三角形是直角三角形

In a sports team each player has a clear role，and there are few occasions _____ members are confused or uncertain of their roles

A．which

B．that

C．when

D．how