Root development is promoted by

Options

A. Auxin
B. Gibberellin
C. Ethylene
D. Abscisic acid

Answer

To determine what promotes root development, we will analyze the options provided:

1. **Auxin**: Auxin is a well-known plant hormone that plays a crucial role in root development. It promotes the initiation of roots in stem cuttings, making it essential for vegetative propagation. Auxin also aids in the growth of pre-existing roots and the branching of roots, enhancing overall root development.

2. **Gibberellin**: Gibberellins are another class of plant hormones, primarily involved in promoting stem elongation, seed germination, and flowering. They do not specifically promote root development.

3. **Ethylene**: Ethylene is a gaseous plant hormone that primarily regulates fruit ripening and can influence other processes such as leaf abscission. It is not directly involved in promoting root development.

4. **Abscisic Acid**: Abscisic acid (ABA) is often referred to as a stress hormone. It helps plants respond to stress conditions, such as drought, by regulating various physiological processes. However, it does not promote root development.

Based on the analysis of the options, the hormone that promotes root development is **Auxin**.

### Final Answer:
**Root development is promoted by Auxin.**