Explanation:
Inhibitory substances play a crucial role in governing seed dormancy. These substances prevent germination until the conditions are favorable for the seed to grow. Among the given options, gibberellic acid (option C) is not an inhibitory substance governing seed dormancy.

Phenolic Acid:
- Phenolic acids are a class of compounds that are derived from benzoic acid.
- They have been found to inhibit seed germination by interfering with various physiological processes, such as membrane permeability and enzyme activities.
- Phenolic acids are known to accumulate in the seed coats and inhibit the production of gibberellins, which are essential for seed germination.

Para-ascorbic Acid:
- Para-ascorbic acid, also known as Vitamin C, has been found to have inhibitory effects on seed germination.
- It acts as an antioxidant and reduces the formation of reactive oxygen species (ROS) that are required for the initiation of germination.
- By reducing the levels of ROS, para-ascorbic acid delays the onset of germination and maintains seed dormancy.

Gibberellic Acid:
- Gibberellic acid is a plant hormone that promotes seed germination and plant growth.
- It is involved in breaking seed dormancy by stimulating the production of hydrolytic enzymes that degrade stored reserves in the seed.
- Gibberellic acid also regulates the synthesis of alpha-amylase, an enzyme responsible for breaking down starch into sugars, which are essential for seedling growth.

Abscisic Acid:
- Abscisic acid is a plant hormone that plays a critical role in inducing and maintaining seed dormancy.
- It inhibits seed germination by blocking the synthesis of gibberellins and promoting the accumulation of storage compounds in the seed.
- Abscisic acid also controls the water potential and prevents water uptake by the seed, further maintaining dormancy.

Conclusion:
Among the given options, phenolic acid, para-ascorbic acid, and abscisic acid are inhibitory substances governing seed dormancy. Gibberellic acid, on the other hand, is a growth-promoting hormone that breaks seed dormancy.