Why were many medieval monasteries wealthy

Medieval monasteries were very powerful and wealty institutions which even had moveable and landed properties. They were centres of education and culture. Education was not cheap at medieval times, so only wealthy people could afford it for themselves and their children. Also there were a lot of rich patrons and charity givers who tried to help and support monasteries with money and goods. 

It's most likely choice a, it makes the most sense in my opinion.