Answer:
The correct option is D. The form of a trait that seemed to "disappear" during his first set of experiments "reappeared during his second set of experiments.
Step-by-step explanation:
Gregor Mendel was an Austrian monk and his findings in genetics led to the foundation of this field. Hence, he is known as the father of genetics.
To study the patterns of inheritance, Mendel used pea plants and took seven traits of the plant into consideration.
Mendel observed that when two parent pea plants (P1 and P2) were crossed, the F1 progeny was similar to one of the parents (say P1). He wondered whether the traits of the other parent would be found in any other progeny. He then self-fertilized F1 pea plants and found out that some of the F2 progeny has traits of the other parent (P2). He hence realized that some of the traits are recessive.