Answer:
A. All possible combinations of alleles in the gametes produced by one parent are written along the top edge of the square
Explanation:
You begin with a square. Then, following the principle of segregation, all possible combinations of alleles in the gametes produced by one parent are written along the top edge of the square. The other parent's alleles are then segregated along the left edge. Next, every possible genotype is written into the boxes within the square, just as they might appear in the F2 generation.