Tutoring: show the source page before quizzing on a new skill

Moving to a new exam skill with a recipe and a partial equation lost the student, who said they didn't know what I was getting at. What fixed it was rendering the actual exam page with pdftoppm, opening it beside the chat with the lecture PDF, and stating in plain words what the question asks. Then reduce the task to a table of options with some rows already worked. Announce topic switches explicitly too, because the student asked twice whether we had changed skills.