选择单词,补全短文
hot China winter people old east
Shanghai is the biggest city in ____.It's in the ____ of China. It's got a lot of ____.It's an ____ city. It's very ____ in summer and it's cold in ____.
如图在⊙O中,弦AB=8,OC⊥AB,垂足为C,且OC=3,则⊙O的半径( )
设变量x,y满足约束条件x≤2y≤xx+y≥2则目标函数z=2x+y的最小值为( )