D
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
Gregor Mendel studied ratios related to traits passed from parent pea plants to offspring pea plants. Mendel used large numbers of plants to avoid "sampling error." This changed the way scientists studied genetics because it included ideas of

### Choices:
A. nuclei and DNA.
B. atoms and molecules.
C. ecology and environment.
D. mathematics and probability.

### Answer:
