桥式起重机的桥架通常有（）等构件组成。
A、主梁
B、端梁
C、支腿
D、走台、栏杆
参考答案：A, B, D
----Mr. Li told me once he had a fall and broke his leg .
----_______was that.
A Since when B For how long C How long ago D How soon
血气分析标本如果接触了空气，则（）
A.PCO2下降
B.PCO2升高
C.pH下降
D.pH升高
E.不能确定
