Answer:
the ventilator between Helen's room
Explanation:
sherlock Holmes discovered it
Us is correct answer. Us is a pronoun. Direct object is a word or group of words that is acted on by a subject.
For Example of direct objects: Monica hit the ball. Raul carried his books in a backpack.
Hope this helps, and Thank you.
That’s one rule you can search up the passage and look for context clue in it.