(p.126, The African American and the Settling of the West, Sarah Nichols and Marie Hernandez, ed.Aaron Wilds.)
When I was teaching through UCSC Extension, one of the students asked if I would meet her outside of class for intensive, one-on-one instruction in editing. I agreed. Turns out, she'd been recently hired as an editor by a major player in the industry, and she now found herself in over her head because, actually, she couldn't edit. Her background? She'd been a massage therapist who'd taken to computers when the desktop models first came out, and so she'd begun a small desktop publishing business. As she worked with the various pieces clients gave her, she began to make little corrections here and there. Soon, she was calling herself an editor. (After all, she was making changes in someone else's text, wasn't she?)
A dependent clause is a clause that cannot stand on its own. This means that it does not have a subject that matches a verb to form a complete sentence or thought. The correct answer for this case, would be A.
In the clause, “during intermission, while we were discussing the performance” there are prepositional phrases that need to be accompanied by an independent clause to make a complete sentence.
A way to potentially complete this sentence would be “ during intermission, when we were discussing the performance, we ordered a popcorn from the concession stand in the theater.”
She learns that she must invest more time in practice