已知集合A={1,2,3,4,5},B={4,5,6,7},则A∪B等于 [ ]
A.{4,5}
B.{1,2,3,4,5,6,7}
C.{1,2,3}
D.{6,7}
答案:B
-Has Tommy finished his homework yet?
-I have no idea; he ____ it this morning.
A.was doing
B.had been doing
C.has done
D.did
辅助功能M代码以地址符M接()组成。