Read the following passage and Choose the correct word or phrase that best fits each of the numbered blanks.

It's quite rare to meet teenagers who don't like sports. When you are young, you know how important (1)______ 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 (2)______ 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 (3)______ 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 (4)______ 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 (5)______ to get a good job. Somehow, it doesn't seem fair.

... if you want to be healthy and strong, and for that reason you often concentrate on just one sport with so (2) _____ enthusiasm that in the end you can't live without it.