Somebody help me!! I’m doing the book Harry Potter and the Sorcerer’s Stone!

I already did number one.
2. Brainstorm details about the book in order to identify a scene, a chapter, a dialogue exchange — any part of the book that affects the whole story. You can make a list, create a cluster diagram, or free write.
3. From your brainstorm in question 2, identify a part of the book that affects the whole. Briefly describe it and its effect on the story.

When the Great Hall opened in 1897, visitors marvelled at the beauty created by fifty American painters and sculptors.

An introductory subordinate clause is found at the beginning of a sentence, uses a subordinate conjunction, contains a subject and verb, and is dependent on the rest of the sentence. The subordinate conjunction in this clause is "when". It joins the opening of the Great Hall with the visitors reaction. The subject of the subordinate clause is Great Hall, and the verb is opened. In the other options, the subject, verb, or subordinate conjunction is missing.