A prepositional phrase is such a phrase which begins with a preposition (on, under, over, etc) and ends with a noun, pronoun, gerund, phrase etc.
So here, the correct sentence will be "On the stage the members of the orchestra began to tune their instruments".
Answer: 1. what is the plot and structure.
Explanation:
All except becoming famous
Yes, commas are used for clauses that help to provide a fuller picture, even when not necessary. Dashes can be used for a similar purpose as they are used here, but i don't believe it's appropriate in this sentence. Parentheses can only be used for information that can be completely written off without having any effect on the sentence.
