During Mendel's first set of experiments, all the plants' F, offspring expressed the same version of the studied trait. Which of the following best describes
these experiments?

A. Mendel allowed true-breeding plants to self-pollinate.

B. Mendel observed crosses that took place naturally in his gardens.

C. Mendel crossed true-breeding plants with different versions of a
studied trait.

D. Mendel crossed plants that all expressed the same version of a
studied trait