Read the following passage and mark the letter A, B, C, or D to indicate the correct word for each of the blanks 

It's quite rare to meet teenagers who don't like sports. When you are young, you know how important (25) ___ to do physical exercise if you want to be healthy and strong, and for that reason you often concentrate on just one sport with so (26) ___ enthusiasm that in the end you can't live without it. The problem is, though, that as you grow up you have less and less spare time. At your age you have to study harder if you want to get good marks to go to university, with perhaps only one afternoon a week to do any sport. This happens just when you are at the best (27) ___ for many sports, such as gymnastics and swimming. By the time you finish all your studies you will probably be too old to be really good at sports like those, but if you spend enough time on (28) ___ while you are young, then one day you will find that you are very good at your sport but too old to study, and you will find it (29) ___ to get a good job. Somehow, it doesn't seem fair.