Explanation:

The word "agent" is a common noun that refers to a person or thing that takes action or has the power to act. In this case, we are looking for the correct abstract noun form of "agent."

Abstract Nouns:
Abstract nouns are nouns that represent ideas, concepts, or qualities rather than physical entities. They cannot be perceived through the five senses and are often intangible.

Options:
a) agency
b) agenda
c) agents
d) agentment

Analysis of Options:
a) agency: This is the correct abstract noun form of "agent." It represents the state or condition of being an agent or the capacity to act as an agent. It is derived from the original noun and accurately reflects its abstract concept.

b) agenda: This is not the correct abstract noun form of "agent." It refers to a list or plan of things to be done or considered. While it is related to the concept of action, it is not directly derived from the noun "agent."

c) agents: This is not the correct abstract noun form of "agent." It is the plural form of the original noun and refers to multiple individuals or things that act as agents.

d) agentment: This is not a valid word and does not accurately represent the abstract concept of "agent."

Conclusion:
The correct abstract noun for the word "agent" is "agency" (option a). It accurately represents the abstract concept of being an agent or having the capacity to act as an agent.