Cane toads are large, nonnative, poisonous toads in Australia. After cane toads entered Australia, scientists observed that the average head size in a
population of toad-eating snakes was getting smaller. Snakes with smaller
heads are not able to eat the large cane toads. What type of situation is this?
O A. Disruptive selection
B. Species richness
C. Directional selection
D. Genetic variation

The answer you are looking for is C

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

if you look up in the top right corner you'll see your current profile picture, click than click "view profile" you'll be able to change it there.