A dioecious flowering plant prevents both

Options

A. Autogamy and xenogamy
B. Autogamy and geitonogamy
C. Geitonogamy and xenogamy
D. Cleistogamy and xenogamy

Explanation

To solve the question regarding what a dioecious flowering plant prevents, we can break it down step by step.

### Step-by-Step Solution:

1. **Understanding Dioecious Plants**:
- Dioecious plants are those that have unisexual flowers, meaning that individual plants are either male or female. This means that one plant will produce only male flowers, and another plant will produce only female flowers.

2. **Identifying Types of Pollination**:
- **Autogamy**: This is self-pollination, where pollen from a flower fertilizes ovules of the same flower. This is not possible in dioecious plants because they do not have both male and female flowers on the same plant.
- **Xenogamy**: This is cross-pollination, where pollen from one plant fertilizes the ovules of another plant. Dioecious plants can still undergo xenogamy since they have separate male and female plants.
- **Gytenogamy**: This involves pollination between different flowers of the same plant. Since dioecious plants do not have both types of flowers on the same plant, gytenogamy is also not possible.
- **Clistogamy**: This refers to self-pollination in closed flowers. Since dioecious plants do not have both male and female flowers on the same plant, clistogamy is not applicable.

3. **Conclusion**:
- Since dioecious plants cannot perform autogamy (self-pollination) and gytenogamy (pollination between flowers of the same plant), they prevent both of these types of pollination.

4. **Final Answer**:
- The correct option is **B: autogamy and gytenogamy**.