Which word must be able to switched with the because for it a conjunction?

The word that can be switched with "because" to create a conjunction is "since".

Here's why:

* Because and since are both subordinating conjunctions that introduce dependent clauses.

* They both express a cause-and-effect relationship.

Example:

* Because it was raining, we stayed inside.

* Since it was raining, we stayed inside.

Both sentences convey the same meaning: the rain caused us to stay inside.

Let me know if you have any other questions!