某一抛物线开口向下，且与x轴无交点，则具有这样性质的抛物线的表达式可能为______（只写一个），此类函数都有______值（填“最大”“最小”）．

_______it is to jump out of an airplane at 10,000 feet!

A．What an exciting experience

B．How exciting experience

C．How an exciting experience

D．What exciting experience