完形填空。阅读下面短文，从短文后所给各题的四个选项（A、B、C和D）中，选出可以填入空白处的最佳选项。
When Edison invented the light bulb, he tried over 2000 experiments __1 he got it to work. A young reporter asked him how it felt to 2 so many times. He said, "I never failed once. I invented the light bulb. It just 3 to be a 2000-step process."
