"each lymphocyte has thousands of receptor proteins in its membranes. what is the job of these receptor proteins? "

Some of these receptors bind to antigens in the blood. The antigen are then endocytosed and identified.  Some of the receptors such as the MHC II are used in antigen-presentation. They display the antigen for identification and activation of other lymphocytes.

i'm gonna put a couple so you can chose from

explanation:

if you know the fur color of the offspring mice, you can use the ratios to identify the genotypes of the parents.

if either parent mouse passes a dominant allele, the offspring will have black fur.

if the parental mice has two different fur color (i.e white and black) , the color of the offspring's fur would be either black, white, or the combination of both (grey)

hope this : )

option number one would be youre best option