Asecondary immune response differs from the primary immune response in that:
a. it is more rapid than the primary response and results in higher antibody levels.
b. it is slower than the primary response and doesn’t change the antibody levels.
c. it occurs at the same time as the primary response but results in a decrease in antibodies.
d. it only occurs in hyperallergic reactions and results in a decrease of antibodies.

Option A,  it is more rapid than the primary response and results in higher antibody levels.

Explanation:

When an antigen contacts the immunity system for the first time  it leads to a primary immune response. Since it is the first interaction, it requires more time   to produce effect.

While a secondary response occurs when the same antigen attacks the same person second , third or n number of times. During secondary response, the body already has a memory of primary immune response and thus it is faster.

Hence, option A is correct

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.