Which one of the following growth regulators is known as stress...

Abscisic acid (ABA) is also known as the stress hormone, is produced during drought, water stress, and any other environmental stress conditions.
This hormone is a dextro-rotatory sesquiterpene-derivative and is synthesized from xanthophylls via the mevalonic acid pathway in the plants.
This hormone is a plant growth inhibitor. When the plant is in water stress, more amount of ABA is synthesized and secreted from the leaves. The transport of this hormone is via diffusion or even via conducting elements. It is an anti-transpirant as it closes the stomata.