Identify the best answer:
 
1. The formula to find average atomic mass is
 
a. ∑Massofisotopes×%Naturalabundance100
 
b. ∑Massofisotopes×100%Naturalabundance
 
c. %Naturealabundance×100∑Massofisotopes
 
d. ∑(Massofisotopes)100
 
2. Which isotope is used to study blood circulation in the body?