水位表的上部可见边缘应比最高安全水位至少高（）。
A、25mm
B、35mm
C、45mm
D、50mm
参考答案：A
At three thousand feet, wide plains begin to appear, and there is never a moment when some distant mountain is not ______.
A．on view
B．at a glance
C．on the scene
D．in sight
T细胞的表面分子是（）。
A.CD3
B.CD19
C.KIR
D.MHC－II
E.IL－2
