In Medieval Times, Leeches Were Commonly Used as a Remedy

In Medieval times, leeches were commonly used as a remedy for someone who was ill. What was the belief behind this widespread practice?

A) Leeches were thought to calm people because the feel of them was soothing on the skin.
B) It was believed that leeches injected the body with life-giving properties.
C) Leeches were believed to be creatures of God and hence able to bestow spiritual protection against disease when properly administered.
D) People who were ill were often believed to have an imbalance of fluids, such as blood, and that leeches could help drain the excess.