下列现象属于生物应激性现象的是（　　）

A．避役的体色与变化的环境保持一致

B．竹节虫的形态与竹节相似

C．蝗虫的体色与绿色的青草一致

D．黄蜂身体上黄黑相间的条纹

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