Why is it important to get enough sleep each night? a. because sleep requirements may interfere with exercise schedules b. because adequate sleep guarantees a stress free day c. because adequate sleep is as important to fitness as exercise and healthy eating d. because sleep requirements may interfere with nutrition requirements

C. Because Adequate sleep is as important to fitness as exercise and healthy eating! 

Sleep affects just about everything you do

It is important to get enough sleep each night because, C, it's just as important. When you sleep your muscles and your brain get to shut off and heal. This is where most muscle building comes from. 
When you workout you're giving your muscle tiny fractures, the reason you get bulkier is that your body rebuilds what was lost in sleep. If you don't get adequate sleep then your muscles won't heal as well or correctly.

The answer would be age 18.