若x+y=9且xy=16,求x2+y2
解:x2+y2=(x+y)2﹣2xy,
=92﹣2×16,
=49.
I'll take_____of the cameras, one is for my brother, the other is for Jim.[ ]
A. either
B. both
C. all
食管癌大多是()。
A.腺癌
B.鳞状细胞癌
C.印戒细胞癌
D.粘液腺癌
E.小细胞未分化癌