Your question and Emma's response makes me see that your question might be confusing.
Collapsed Topics provides "open all" and "close all" quick buttons. There is no way to say "Open 1, 3, and 7" with one click. If anyone wants to see only 1,3, and 7 open, I would first do a "close all" and then individually uncollapse section 1,3, and 7.
But if you really don't want section 2, for example, showing to students, then follow Emma's advice.
(Your request is not strange at all. This Collapsed Topics feature does not exist in any other major LMS, BCD, so it can catch some folks by surprise. I am one who loves Collapsed Topics and don't see why BCD have not provided similar functionality.)