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Correct answer: C. A project holding the PDF, with study mode used inside it for each evening's session
Explanation
The principle — a task with several requirements is usually solved by combining features rather than by finding one that does everything. Reading the requirements separately is what makes the combination obvious.
Why the key is correct — three requirements, and the arrangement meets each with the feature built for it. The material has to persist across evenings, which is what a project does: OpenAI describes projects as workspaces that keep chats and uploaded reference files together for a long-running effort, so the PDF is uploaded once rather than nightly. The revision has to test rather than tell, which is Study Mode: instead of only giving a final answer, ChatGPT can ask questions, guide your thinking, explain ideas step by step and check your understanding as you go. And the two compose, because the familiar tools are available inside a project, with study mode named among them. Study Mode is also available on all plans globally, so this works on a free account.
Why the others are wrong — re-attaching the PDF nightly satisfies nothing cleanly and spends uploads against a daily cap, and asking for a summary hands over answers, which is the opposite of the stated requirement. One long conversation keeps the material but accumulates four evenings of questions in a single thread, and it still does not make the assistant quiz rather than tell. The custom instruction is the most tempting wrong answer: it does address being quizzed, but it applies to every conversation for the whole period, including unrelated ones, and it leaves the notes being uploaded again each evening.
Remember this — split a requirement list before choosing a tool. Persistence of material is a project question, the style of the interaction is a mode question, and scope of a preference is an instructions question. Answering them separately usually produces a better arrangement than looking for a single feature that seems to cover everything.
Sources — OpenAI's Projects in ChatGPT and Using Study Mode in ChatGPT articles.
Sources
“Instead of only giving a final answer, ChatGPT can ask questions, guide your thinking, explain ideas step by step, and check your understanding as you go.”
“Projects are smart workspaces that keep everything related to a long-running effort in one place.”
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