About 20 percent of the work ____done yesterday.
A.are
B.is
C.were
D.was
答案:D
胃内最易出现溃疡的部位在:()
A.胃底
B.胃大弯侧
C.幽门管
D.胃角
E.胃窦
永久性普通螺栓紧固应牢固、可靠,丝扣至少外露()扣。
A.1
B.2
C.3
D.4