Here are the answers to your questions:
Question 1: What is a noun clause?
Answer: a dependent clause that functions as a noun
Question 2: How are clauses and phrases different from each other?
Answer: A clause contains a subject and a verb while a phrase does not.
Question 3: Which sentence has a participial phrase?
Answer: Students planning to study engineering must first take an introductory course.
Question 4: What kind of phrase or clause is used in the beginning of this sentence and what does it modify?
Answer: a participial phrase that modifies sprinter
Question 5: Which sentence combines these two sentences together using an adverbial clause while keeping the original meaning of the two sentences?
Answer: Before we go on vacation, we must make reservations for our flights and hotels.
Feel free to ask more questions if you need further assistance!