The correct answer is C. Sleep.
When you put your computer to sleep, it saves your work to the hard drive and then turns off most of the power to the computer. This saves energy and helps your computer last longer. When you wake your computer up from sleep, it quickly returns to the state it was in before you put it to sleep.
A. Shut Down turns off your computer completely. This means that all of the power is turned off, and your computer will not save any of your work. When you turn your computer back on, you will need to start from scratch.
B. Restart turns off your computer and then turns it back on again. This is similar to shutting down your computer, but it also gives your computer a chance to run some maintenance tasks.
D. Hibernate is similar to sleep, but it saves your work to the hard drive and then turns off all of the power to the computer. This saves even more energy than sleep, but it also takes longer to wake your computer up from hibernation.