已知2x+y=8，xy=7， 那么代数式3xy-4x-2y+1的值为（ ）。
6
下列运算中，正确的是（ ）
A．a3÷a2=a
B．a2+a2=a4
C．（ab）3=a4
D．2ab-b=2a
Although I have traveled to many scenic spots before, ________of them are as attractive as the one
I visited this summer vacation.[ ]
A. any
B. none
C. neither
D. all
