In the ceremony, our headmaster required       students to improve our competitive awareness in modern society.

A．we

B．us

C．our

D．ours

阻塞性肺气肿支气管炎型的临床表现，下列哪项是正确的（）

A.发病年龄较轻

B.多无发绀

C.喘息明显，多呈持续性

D.X线胸部X线片呈肺纹理减少

E.静息时PaO轻度降低