口对口人工呼吸时吸入的氧气浓度为()
A.10%
B.16%
C.21%
D.25%
E.30%
参考答案:B
---How was your climb up Mount Tai?
---I didn’t believe I could do it I got to the top.
A.until
B.unless
C.after
D.when
销毁旧公章要登记造册,经上司批准后,要有()人监督。
A、1
B、2
C、3
D、4