No it is not.
The word "that" can be a conjunction, determiner, pronoun or adverb.
No, the word "I" is not a preposition. "I" is a pronoun, specifically a subject pronoun that is used to refer to oneself.
No the word every is not a preposition.
No, the word "early" is an adverb, not a preposition. It is used to describe the timing of an action or event.
No, the word "when" is not a preposition. It is an adverb or a conjunction used to indicate time or a condition.
No, it is not a preposition. The word explore is a verb.
No, it is not a preposition. The word thing is a noun.
Yes, the word among is a preposition.
Yes, "afterwards" is an adverb, not a preposition. It is used to indicate a time that is after a particular event or period.
Yes, the word "within" is a preposition. It is commonly used to express something located inside or contained within a particular area or boundary.
No, the word "away" is not a preposition. It is typically an adverb that describes movement or distance.
No, it is not a preposition. The word travelers is a plural noun.
No, it is not a preposition. The word surrounds is a verb form.