A dioecious flowering plant prevents both

Options

A. autogamy
B. autogamy and geitonogamy
C. geitonogamy and xenogamy
D. cleistrogamy and xenogamy

Answer

### Step-by-Step Solution:

1. **Understanding Dioecious Plants**:
- Dioecious plants are those that have unisexual flowers, meaning that individual plants are either male (staminate) or female (pistillate). This separation of sexes means that one plant cannot produce both pollen and ovules.

2. **Identifying Pollination Types**:
- **Autogamy**: This is a form of self-pollination where pollen from the anther of a flower fertilizes the stigma of the same flower. Since dioecious plants have separate male and female flowers, they cannot undergo autogamy.
- **Geitonogamy**: This is another form of self-pollination where pollen from one flower fertilizes the stigma of another flower on the same plant. Again, since dioecious plants consist of separate male and female plants, geitonogamy is not possible.
- **Xenogamy**: This is cross-pollination where pollen is transferred from the anther of one plant to the stigma of another plant. Dioecious plants can undergo xenogamy since they require pollen from a male plant to fertilize the ovules of a female plant.

3. **Conclusion**:
- Since dioecious plants cannot perform autogamy or geitonogamy due to their unisexual nature, the correct answer to the question "A dioecious flowering plant prevents both" is **autogamy and geitonogamy**.

### Final Answer:
A dioecious flowering plant prevents both **autogamy and geitonogamy**.

---