Answer:
A. If seed shape did not have a clearly recessive form
Step-by-step explanation:
To study inheritance patterns, Mendel studied a few characteristics of pea plant -e.g. pea colour, shape, plant height. These characteristics had to be very clear dominant and recessive forms to distinguish between, otherwise detecting the patterns would not have been obvious.
For example, if crossing a wrinkled seed plant with a smooth seed plant made a semi-wrinkled plant, Mendel would not have been able to study the inheritance of dominant and recessive traits.