By what means has the overuse of antibiotics in medicine and agriculture lead to the current global problem of antibiotic resistance? The overuse of antibiotics significantly increases the bacterial mutation rate, causing more antibiotic-resistance mutations to occur.
Humans develop an immunity to antibiotics, rendering them ineffective.
Indiscriminant use of antibiotics selects for resistant bacteria and increases their numbers.
Antibiotic resistance is a fabricated problem used to sell newer and more expensive antibiotics.

the most logical answer would be a

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.