Answer:

Explanation:
The underlined word is "Cage".

Definition of Cage:
A cage is a structure made of bars or wire mesh that is used to enclose or confine animals or prisoners.

Analysis:
To find the word that names a necessary part of the underlined word "Cage", we need to identify the essential component or element that is required for a cage to exist or function properly. Let's analyze the given options:

a) Enclosure: An enclosure is a space or area that is bounded by walls, fences, or barriers. In the context of a cage, an enclosure is necessary as it provides a confined space for animals or prisoners.

b) Prisoner: While a prisoner is a living being that can be kept in a cage, it is not a necessary part of a cage itself. A cage can exist and function without a prisoner inside it.

c) Animal: Animals are the occupants or inhabitants of a cage, but they are not necessary for the existence of a cage. A cage can be empty or used for other purposes.

d) Zoo: A zoo is a place where various animals are kept in enclosures, including cages. However, a zoo is not a necessary part of a cage. A cage can exist outside of a zoo setting.

Conclusion:
Among the given options, the word that names a necessary part of the underlined word "Cage" is "Enclosure" (option A). An enclosure is an essential component of a cage as it provides the structure and boundaries necessary to confine animals or prisoners.