My mother and I are in the shop(商店). We'll buy(买)some fruit. There are many apples, bananas, oranges, pears and watermelons. How much are they? Four yuan for a kilo(千克) of apples. Two yuan for a kilo of bananas. Three yuan for a kilo of oranges. Five yuan for a kilo of pears. One yuan for a kilo of watermelons. We'll take some.

“我们亚洲，山是高昂的头”，这里的“山”是世界的“头”， 那么这座“山”是指（   ）

设x，y满足约束条件$\left\{\begin{array}{c}x\ge 2\\ 2x-y\ge 1\\ y\ge x\end{array}\begin{array}{c}\\ \end{array}\right.$，若目标函数$z=ax+by\left(a>0,b>0\right)$的最小值为2，则$ab$的最大值（  ）