UanM: edit / modify MCQs in the Check Understanding (CU) section

[pahp]

There are some problems with the existing CU MCQs:

1. They give away the answers to the activity
2. the "both" or "neither" constructions are not best practice for MCQs
3. It's not entirely clear to me what the right answer is to Security by Obscurity improvements #2. (E.g., in this context, maybe it would be OK to assume they meant "minutes"?) -- it seems arguable, at least.

I would like the questions to:

1. use best MCQ practices
2. be unarguable
3. not leak exercise content
4. maybe include a code injection example of some kind