X线管阳极靶面的材料一般采用
A．铜
B．铝
C．铅
D．锡
E．钨
参考答案：E
解析：X线管阳极靶面一般都是用高原子序数，高熔点的钨制成。
Mr. Green _______ to Beijing two weeks ago. He ______ there many times.
A．has gone; has been
B．went; has been
C．has gone; went
D．went; went
肾综合征出血热早期休克的主要原因是（）
A.播散性血管内凝血（DIC.
B.心肌损害
C.继发严重感染
D.腔道大出血
E.小血管通透性增加，血浆外渗，血容量锐减
