Does anybody know the answer i need help on this question
The correct answer is A.
An Adverb Clause, also known as Adverbial Clause has the function of an adverb, and, in this case, it answers the question how, and talks about a possible situation and consequences: If you don't buy the tickets in advance, <em>you may not be able to get them</em>. The second sentence is a possible situation in the case of a delay to buy the tickets.
