D. The body will be able to produce the antibodies and memory cells needed to fight disease and recover quickly. Exercise and vitamin C is what creates antibodies and white blood cells that fight diseases. Plus exercise can clear the lungs of any dangerous germs that can cause illness like a cold or flu. And sleeping well and resting would remove any kind of stress one would receive from exercising.
I believe the inability to make saliva would affect digestion drastically. The first phase in the process of digestion comes with saliva - it breaks down some substances in your mouth, because it contains amylase which helps during this process. If it weren't for saliva, you probably wouldn't even be able to swallow food - and even if you did, it would be almost impossible to break it down in your body.
The fact that it's a renewable resource would be the only benefit. All of the others are disadvantages
