艾滋病的主要传播途径为（）
A.性接触传播，经血液传播和母婴传播
B.日常生活和工作接触传播
C.共同进餐和接吻传播
D.注射传播
参考答案：A
The accident happened at nine o'clock in the morning ____ we were all busy with our work. [ ]
A. that
B. which
C. when
D. as
—Are the shoes under your bed?
—_______. [ ]
A. Yes, it is
B. Yes, they are
C. No, it isn't
