Name the part of speech of the underlined word in the following sentence:

A preposition can be defined as a word or phrase used before a noun, pronoun, or noun phrase to indicate direction, time, place, location, spatial relationships, or to introduce an item. Words like "in," "of," "at," "on," are examples of prepositions.

In the given sentence The preposition 'on' is valid since it is used to signify that someone is a member of a club or organization. Here, it is a committee.

Hence, the correct option is D i.e., Preposition