前庭大腺炎主要的治病菌为（）。
A.链球菌
B.葡萄球菌
C.大肠杆菌
D.淋病奈氏菌
E.沙眼衣原体
参考答案：A, B, C, D, E
Frank asked his father ____ a new bike for him and his father said OK.
A．buy
B．to buy
C．buying
D．bought
先化简，再求值：2a(a+b)-(a+b)2，其中
