I am one of those who cannot describe what they do not see. which on is a preposition
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Complete Question:

Which one is a preposition?

of

Explanation:

A preposition can be defined as a word that shows or illustrates the relationship between a pronoun or noun and other words in a sentence. Some examples of a preposition used in various literary works in English language are up, below, after, by, against, for, over, at, to, etc.

The main purpose of a preposition as a part of speech is to introduce an object (of, upon), indicate a timeframe (from, by, over), show direction (to, across, along), location or place (at, up, after, below) and to illustrate the spatial or sequential relationship between two or more things, people, place, etc.

Hence, the preposition in the sentence "I am one of those who cannot describe what they do not see." is the word of. It simply means that the speaker belongs to the category of people without the ability to describe what they cannot or do not see.

B.  Lisa's dad, one of the firefighters in town, was praised as a hero for rescuing a young boy.

Explanation;

Option A is not correct because the subject "Lisa's dad" is singular, but the verb "have been" is plural.

Option C is not correct because the verb part "are praised" is not correct since "are" is plural but the subject "Lisa's dad" is singular.

Option D is not correct because the verb "were praised" is plural and cannot match with the singular subject "Lisa's dad".

Therefore, option B is the only correct option left.