[单项选择题] We are glad to receive your telegraphic order of May 6 ______ regret that we can- not supply

[单项选择题] We are glad to receive your telegraphic order of May 6 ______ regret that we can- not supply the goods ______ the end of May.

A．but, by

B．and, by

C．but, for

D．and, for