Slide mask for questions

Good morning all

I'm trying to create all a series of questions in a question bank.

I would like my question slides to all look the same. For this, I will modify a slide master for the questions

but in the slide masks, I don't see how to change the shape of the checkboxes for example. For example, I want all my checkboxes to be big

likewise, I don't understand why when I make return masks in which I want a minimum of things (no continue button for example because automatic passage after 3 seconds), the software adds them to me anyway?

thank you in advance

FRançois