The principle of common descent explain why
a.well adapted species have many off spring
b.conditions in an organisms environment ensure the organisms survival
c.birds and reptiles share a number of inherited characteristics
d. tigers are so different from cheetahs

The correct answer would be c. birds and reptiles share a number of inherited characteristics.

In evolutionary biology, the principle of common ancestors or descent explains how different groups of organisms share a common ancestor.

In other words, different groups of organisms are believed to evolve from a common ancestor.

The groups which share recent common ancestor share a number of common inherited characters.

The groups which share distant common ancestor share less common characters.

Thus, birds and reptiles share a number of characters as they have evolved from common descent or ancestor.

i think it would be a mutation inhibiting human immunodeficiency virus from entering a host cell cause;

a mutation causing uncontrollable cell growth in tissue would result in a tumor like formation growing on certain parts of the body

a mutation resulting in partial or complete loss of chlorophyll pigments in plants would result in the plant not being the actual color, the chlorophyll (chlorin) absorbs yellow and blue wavelengths of light while reflecting green so the plant would most likely be a color the plant is absorbing or a color we cant see that is on the electromagnetic spectrum

a mutation resulting in a squirrel being born without ovaries would probably kill the squirrel :'(

anyways hope i helped :