已知全集U={1，2，3，4，5}，集合A={x|x2-3x+2=0}，B={x|x=2a，a∈A}，则集合C∪（A∪B）=（ ）
--My father ___________ a letter yesterday, but I’m not sure if he has finished it.
---Why not ask him about it ?
A．wrote
B．was writing
C．has written
D．writes
（）在根上无不定芽，发芽部位在根茎上，分割时必须每块根连带着芽分开切取，再行栽植。
A.美人蕉
B.仙客来
C.大丽花
D.唐菖蒲
