Concept:"in which" is a relative pronoun phrase used to introduce a clause that gives more information about a place, situation, or thing.
Explanation:Relative pronoun phrases like "in which" join a descriptive clause smoothly to a noun.
The word "what" cannot be used as a relative pronoun after a noun.
"from where" suggests movement or a starting point, so it does not fit a general completing role.
"in that" means "because" and acts as a conjunction, not a relative phrase.
Therefore, the correct best completion is "in which".
For example: "The room in which the meeting was held is large."
This shows how "in which" relates clearly to the place or situation described.
Answer:A. in which