I believe it would be C. Cracking a rib.
Because
- CPR doesn't involve the arms
- Headaches can happen at any age
- Not finding a pulse can happen with any person
- Cracking a rib would make the most sense to me due to that bone mass or density decreases as a person ages, the bones lose calcium and minerals causing them to deteriorate and become more brittle, which may result in them becoming easily breakable.
This is only my guess though, so don't take my word for it.
Hope it helps at least a little. (:
