To keep out dirt and other bad things
I think its B because Charlie is overweight and should start a exercise routine and diet but his caliper test doesn't make sense since his BMI is so high.
The best possible way to verify claims a manufactures makes about a supplement's safety and effectiveness would be to go to the manufactures website and look at the reviews, research the studies behind their product and ask around. Since supplements are usually regulated by the FDA, manufacturers are basically given the "honor system" to provide accurate information to consumers. Doing your own research will help immensely. If you ever see something on a supplement(s) that says, "This statement has not been verified by the Food and Drug Administration", I would take it at my own risk.
I think you are looking for the answer of: digestion.
Hope this helps! <3