In cocker spaniels, solid color (A) is dominant over spotted (a), and
black coat color (B) is dominant over red (b). If two solid black dogs
were crossed several times and the total offspring were eighteen solid
black and five spotted black puppies, the genotypes of the parents
would most likely be
a. Aa Bb x AA Bb 
b. Aa BB x aa Bb 
c. Aa Bb x Aa Bb 
d. AA BB x Aa Bb 
e. aa Bb x AA Bb

Hi Operator,

Me again.  I just love these genetic cross questions!

This one is b: AaBB X AaBb

Let's approach this one from the point of view of knocking out our
options.  First of all, all the offspring are solid black, which means
at least one of the parents has to be homozygous for the dominant (B)
allele - the puppies may be heterozygous, we really don't care.  We
also don't care whether the other parent of homozygous or
heterozygous, since all the puppies will end up black either way. 
That means that the answer has to be either b or c.

Second, we know that roughly 1/4th of the offspring (remember that in
real life statistics is approximate) are homozygous for the recessive
spotty allele (a).  That means that we have a classic 3:1 ratio of
phenotypes, indicating two heterozygous parents.

Thus, our answer is AaBB by AaBb.

Yours, Librariankt