—Was it because the traffic was very heavy during the rush hour _______ you were late again?

—Well, I’m afraid so.

A. when                B. that                          C. why                         D. how

Was it because the traffic was very heavy during the rush hour ________ you were late again?

Well, I'm afraid so.

[　　]

--Was it because the traffic was very heavy during the rush hour _____ you were late again?

--Well, I'm afraid so.

[　　]

A．when　　　 B．that

C．why　　　　D．how