What do you usually do _____ the evening after supper? [ ]
A. on
B. at
C. of
D. in
答案:D
对于坐标平面内的任意两点P1(x1,y1),P2(x2,y2),定义运算“⊗”为:P1⊗P2=(x1,y1)⊗(x2,y2)=(x1x2-y1y2,x1y2+x2y1)若点M(x,y)(-2≤x≤-1),点N的坐标为(x,y)⊗(1,1),则点N到直线x+y+2=0距离的最大值为______.
一般认为,在我国北方干旱地区土壤盐基饱和度大,土壤Ph也较高