What is the object of the preposition in sentence?

He will walk alone from his office.

1)alone
2)children
3)under
4)the

I say (1) alone

No. Alone is the direct object.

Which word is the preposition?

http://www.chompchomp.com/terms/preposition.htm

An OBJECT of anything is a noun. “Alone” is not a noun.

You noticed that too! I wonder if the choices match another question.

Probably! Very strange, but that's the only thing that makes sense.

Writeacher is right. Alone is not a direct object; it is not a noun.

Alone is an adverb, defining how he walks. None of the choices is the object of the preposition.

Reed is right. None of the choices is the object of the preposition in this sentence. In fact, none of the other words to choose from are even IN this sentence! ¯\_(ツ)_/¯