How can toxic chemicals affect human immune, nervous, and endocrine systems?

Some toxic chemicals can make the body shut down and not function properly.

Explanation: Some gasses alter your cellular membrane like carbon monoxide or cyanide which affects your brain functions

The toxins reduce the amount of cells which are capable of suppressing the immune response. So multi-resistant strains, which produce very high levels of enterotoxin, becomes even more dangerous.

For endocrine system the chemicals are linked with developmental, reproductive, brain, immune, etc...

Hope it helps you.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.