Self-antigens are not recognized and attacked by the T cells.
Explanation:
In immunology, the antigens are those substances which are bound by the antibodies. The antigens can be originated from within the bodies, known as self antigens or from outside the body, known as non-self antigens. The immune system identifies and attacks non-self invaders or the foreign harmful objects present in the body. It does not attack the self-antigens under the normal conditions. This is due to the negative selection of T cells of the thymus.
Natural selection is the mechanism in which organisms inherit the traits that are necessary for survival and thus change. Those who do not have these traits die.
A dihybrid cross would be crossing 2 (usually linked) traits in the same punnett square, while a trihybrid cross is with 3 traits. Since he's only studying 1 trait (tall vs. short) the answer is C, a monohybrid cross.
