复种中，收完上茬在种植下茬，属于（）
A.接茬复种
B.移栽复种
C.套作复种
D.再生复种
参考答案：A
—Why are you so _______?
—Don't you know? Our basketball team wins![ ]
A. excited
B. sad
C. cold
D. sharp
曲面z=χ2+y2在(-1，2，5)处的切平面方程是()
A.2χ+4y+z=11
B.-2χ-4y+z=-1
C.2χ-4y-z=-15
D.2χ-4y+z=-5
