I would say a because he ran too much but that would be just me I think he hurt his knee from running too much more exercise but probably just aggravate his condition I could be wrong but this is what I think
1-3 year olds should have 2g of salt a day.
4-6 year olds should have 3g of salt a day.
7-10 year olds should have 5g of salt a day.
11 year olds+ should have 6g of salt a day.