由于管网内流通的能源介质的性质不同，所使用的阀门代号也有差别，“A”表示的阀门是（）。
A.闸阀
B.截止阀
C.球阀
D.安全阀
参考答案：D
Wang Lin is a football fan. He _____ the opening ceremony of the 19th FIFA World Cup in South Africa
at 5 o'clock this morning. [ ]
A. was watching
B. has watched
C. watches
D. would be watching
超急性排斥反应有
A．广泛小血管炎伴血栓形成B．血管内膜纤维化C．急性血管炎D．急性间质炎
