有关氮循环中微生物代谢类型、相关生理过程及生态地位全部正确的一组是（）
A.A
B.B
C.C
D.D
参考答案：A
He usually goes to school by bus, but he______ the bus yesterday. [ ]
A. didn't took
B. didn't take
C. not took
D. took
下列哪些是内伤头痛的病因
A．饮食不节
B．房劳过度
C．禀赋不足
D．病后体虚
E．跌仆损伤
