What happens next in this paragraph?

How to operate a wheelchair safely outdoors
Stay on even surfaces.
Uneven surfaces can make any wheelchair get off balance. Even when someone is pushing a wheelchair, an uneven surface can cause harm.
Select from:
[a]. Try to stay within an even surface if you're able to. Avoid climbing or leaning on bare rocks or concrete.
[b]. When you're walking around with someone, always make sure that you stay on a flat surface without access to a handrail. That way, you can avoid debris that might injure someone in the event of a fall.
[c]. Make sure you stay on this surface and do not place yourself in harm's way. Wear protective clothing when you use your wheelchair.
[d]. Users and caregivers alike need to stick to slopes that only go up to a gradient of 20% and are dry, solid, and straight. Avoid inclines, slopes, staircases, and curbs.
[d].