When the sentence use the conjuction so here it should be happened at the same time.
It is the word where the words, phrases, and the clauses should be connected. Also, the word should be applied for linking the clause or the sentence or for coordinating the words in the similar clause.
Therefore, we can conclude that When the sentence use the conjuction so here it should be happened at the same time.
hence, the option a is correct.
Learn more about conjunction here: https://brainly.com/question/24002903