口对口人工呼吸法即使操作正确，吸入氧浓度也常低于（）
A.21%
B.18%
C.15%
D.12%
E.10%
参考答案：B
股骨下1/3骨折，易造成（）。
A.股动脉损伤
B.腘动脉损伤
C.皮神经损伤
D.肱静脉损伤
E.坐骨神经损伤
21. He apologized ________ late.
A．to his teacher to arrive
B．to his teacher for arriving
C．at his teacher to arrive
D．at his teacher for arriving
