20) in natural ecosystems, the presence of predators lessens the effects of among the prey. a) competition b) infestation c) parasitism d) symbiosis

The correct answer for the blank is -

A) competition.

The predator population captures, kills and consume the prey (such as Lion eats leopard and other animals) Due to this, the size of prey population is reduced. This will eventually lead to decrease in competition for various resources (such as food, shelter, mates) within the prey population.

the correct answer is b

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.