In paragraph 2, the author explains how having too many germs in your mouth can "end up weakening the heart." Using the passage as a guide, it can be understood that doctors are ()

A.deny 
B.refuse 
C.insist 
D.hide

A. The lower the karat rating, the purer the gold.
B. The higher the karat rating, the more expensive the gold.
C. The higher the karat rating, the less valuable the mixture.
D. The lower the karat rating, the purer the alloy.