Seed dormancy is caused by

Options

A. `C_(2)H_(4)`
B. `ABA`
C. I A A
D. `GA_(3)`

Explanation

**Step-by-Step Solution:**

1. **Understanding Seed Dormancy**: Seed dormancy refers to a state in which seeds do not germinate despite the presence of favorable conditions such as adequate temperature, moisture, and oxygen. This state is crucial for the survival of the species, allowing seeds to wait for optimal conditions for germination.

2. **Types of Seed Dormancy**: There are generally two types of seed dormancy:
- **Seed Coat Dormancy**: This occurs when the seed coat is impermeable to water and oxygen, preventing the seed from taking in the necessary elements for germination.
- **Internal Dormancy**: This type arises from the presence of substances within the seed that inhibit germination, even when external conditions are suitable.

3. **Role of Hormones**: Among the various factors influencing seed dormancy, plant hormones play a significant role. The hormone primarily responsible for inducing and maintaining seed dormancy is **abscisic acid (ABA)**.

4. **Function of Abscisic Acid**: Abscisic acid regulates various aspects of plant growth and development, particularly in response to stress. It helps in maintaining dormancy by inhibiting germination until conditions are favorable.

5. **Conclusion**: Therefore, the primary cause of seed dormancy is the presence of **abscisic acid (ABA)**, which regulates the dormancy state of seeds.

**Final Answer**: Seed dormancy is caused by abscisic acid (ABA).

---