If students do not see clickable bubbles for multiple choice questions or text boxes to answer short answer questions in the questions panel of a text, then students are most likely on a text preview page rather than their assignment.
Text preview is what happens when you search for a text from the library. The URL for text preview pages will contain "/texts" followed by the title of the text.
When they land on this page, a pop-up will appear with the option to go to their assignment. If they exit out of this, they can also click "Go to Assignment" in the questions panel.
Students can only answer and submit the questions after you have assigned the text and students access the assignment through their notification bell or by going to their "My Assignments" page and clicking the assignment to begin it. You can tell when students are on an assignment because they can see Guided Reading Questions and blurred text, if you have assigned guided reading mode, or they can see clickable answers in the question panels for their final assessment questions. The URL for student assignments end with "/student-assessment."
Here is a brief video walking you through the student experience of taking assignments: https://www.youtube.com/watch?v=X5ogjmmZ7qI