Classify each of the following as homozygous dominant, heterozygous, or homozygous recessive.
a. gg
b. rr
c. tt
d. does not include any dominant alleles
e. does not include any recessive alleles

First, we will elaborate the terms that are being used.

Heterozygous:
This means that the organism has a set of alleles which are different from one another. One copy may be for the dominant trait and the other for the recessive one.

Homozygous: 
The organism has two copies of the same allele

Dominant:
An allele that will express itself even if only one copy of it is present. These are usually represented by capital letters.

Recessive:
An allele that requires both copies to be expressed. These are usually represented by lower-case letters.

A: Heterozygous

B: homozygous recessive

C: Homozygous dominant

D: Homozygous recessive

E: Homozygous dominant

Probably a behavioral adaptation