Answer: At the beginning
Explanation: Introductory clauses are dependent clauses that provide background information or "set the stage" for the main part of the sentence, the independent clause. For example: If they want to win, athletes must exercise every day. Because Smokey kept barking insistently, we threw the ball for him.
They can also be placed at the end of a sentence like, "Athletes must exercise every day if they want to win."