完形填空
When I started riding a bike a couple of years ago, I didn't think my involvement（投入）would ever be more serious than sometime short rides．But as I build up 21 , my friends encouraged me to try some 22 trips．The first one to come along was a 150-mile ride, an annual 23 that raises money to fight cancer．
When I registered, the idea seemed excellent to support a 24 cause while riding for a long distance．But 25 the time for the ride approached, my self-doubt gained ground（优势） 26 my determination．As a matter of fact, though I 27 want to raise money for the charity, I didn't really want to bike all those miles for two days 28 ．
The ride began on a Sunday morning, and for the first few hours I felt wonderful．This was just the experience I had imagined, and my spirits were high．But by the end of the day, I felt tired and 29 ．
