Gregor Mendel, the father of genetics, conducted experiments on pea plants (Pisum sativum) and identified seven contrasting traits:
1. Seed shape - Round vs. Wrinkled
2. Seed color - Yellow vs. Green
3. Flower color - White vs. Violet
4. Pod shape - Inflated vs. Constricted
5. Pod color - Green vs. Yellow
6. Flower position - Axial vs. Terminal
7. Plant height - Tall vs. Dwarf
Since all these traits were studied, the correct answer is (D) All of these.