____________ you usually go to school on foot?[ ]
A. Is
B. Are
C. Does
D. Do
答案:D
Air is to us _____ water is to fish.
A.what
B.that
C.which
D.is that
使用人工呼吸器,吸呼比应为
A.1:(0.5~1)B.1:(0.5~2)C.1:(1.0~3)D.1:(1.5~2)E.1:(1.5~2.5)