Questions: Gregor Mendel studied pea plants to determine the patterns of inheritance. What is not a reason Mendel used pea plants in his experiments? Check all that apply. They reproduced sexually. They were drought resistant. They had traits that were easy to observe. They only had two traits to study.

The answer is the second one and the fourth one: They were drought resistant and They only had two traits to study.

Explanation for each option:

• They reproduced sexually.
  This is not a reason that is incorrect. Mendel used pea plants because they reproduce sexually, allowing for controlled breeding experiments and the study of inheritance patterns.

• They were drought resistant.
  This is not a reason Mendel used pea plants. Drought resistance was not a factor in Mendel's choice of pea plants for his experiments.

• They had traits that were easy to observe.
  This is a correct reason. Mendel chose pea plants because they had distinct, easily observable traits, such as flower color and seed shape, which made it easier to track inheritance patterns.

• They only had two traits to study.
  This is not a reason Mendel used pea plants. In fact, Mendel studied multiple traits in pea plants, such as seed shape, seed color, flower color, and pod shape, among others.

In summary, the reasons that are not applicable to Mendel's choice of pea plants are that they were drought resistant and that they only had two traits to study.