治疗伤寒首选的抗生素是（）。
A.喹诺酮类
B.头孢类
C.氨基糖苷类
D.氯霉素
E.复方磺胺甲基异恶唑
参考答案：A
分别以一个直角三角形的三条边所在直线为轴，其余各边旋转一周形成的曲面围成三个几何体，分别求出它们体积。
If he ________ well for his lessons yesterday, he ________ so many difficulties now. [ ]
A. had prepared; wouldn't have
B. had prepared; wouldn't have had
C. prepared; wouldn't have
D. prepared; wouldn't have had
