21时40分是晚上9时40分．______．（判断对错）
21时40分即晚上21时40分-12时=9时40分，
故答案为：√．
水泵的汽蚀余量△hr的含义是（）。
A、水泵的允许吸上真空度。
B、垂直安装尺寸。
C、水泵入口处单位重量的液体所具有的超过气化压力的富裕能量。
D、液体从泵的吸入口到叶轮中心处的压力降。
Even though I have been to her apartment several times before, I still don’t remember （）。
A. which building it is in
B. which the building is in
C. which is it in
D. which building is it in
