Pea plants are tall if they have the genotype TT or Tt, and they are short if they have genotype tt. A tall plant is mated with a short plant. Which outcome below would indicate that the tall parent plant was heterozygous?

a) All of the offspring are short.

b) All of the offspring are tall.

c) The ratio of tall offspring to short offspring is 3:1.

d) The ratio of tall offspring to short offspring is 1:1.

e) There is not enough information to answer the question.