Answer: The correct answer is-
D. both Yy
As per the information given in the question, two yellow squash plants produce 124 offspring upon crossing out of which 93 produce yellow squash and 31 produce green squash.
This indicates that the yellow squash plant is dominant ( depicted by capital letter allele such as Y) over the green squash plant, which is a recessive trait ( depicted by small letter allele y).
A dominant allele mask the expression of recessive allele. There can be two possible genotype for yellow squash plant ( YY and Yy) but green squash plant can be only produced with single genotype that is yy.
In order to produce both green as well as yellow squash plant, parent plants mush be heterozygous dominant (Yy).
Thus, option D) is the right answer.