臭氧(O3)的氧化性很强,下列物质不会破坏大气臭氧层的是( )
A.二氧化硫
B.二氧化碳
C.一氧化氮
D.氟里昂
答案:B
胃十二指肠溃疡大出血的溃疡一般位于()
A.胃大弯
B.胃底后壁
C.胃体后壁
D.胃小弯或十二指肠后壁
E.十二指肠球部前壁
If you are invited for 4:00, you have to be there _ .[ ]
A.at times
B. on time
C. behind time
D. from time to time