The first man _____ across the English Channel would receive

The first man _____ across the English Channel would receive Lord Northcliffe's prize.
A.who was going to fly
B.flying
C.to fly
D.having flown
为什么最佳选C?为什么其他三项不行?
新概念上的原文为：
In 1908 Lord Northcliffe offered a prize of 1000 pounds to the first man who would fly across the English Channel.