Which of the following PGR is also known as anti-gibberellin?

The correct option is C Abscisic acid
Antagonism occurs when a hormone opposes or reverses the effect of another hormone.

Abscisic acid is a growth-inhibiting hormone that causes dormancy and abscission (dropping leaves, flowers, and fruits). It regulates the dormancy of buds, tubers, and seeds by inhibiting the growth process. As ABA inhibits gibberellin-stimulated growth in plants, it is called anti-gibberellin. ABA acts as an antagonist to gibberellin. Dormant seeds germinate when gibberellins overcome ABA.

Auxins, gibberellins, and cytokinins are growth-promoting hormones, whereas ethylene is a gaseous PGR that shows growth stimulation and inhibition activities.