Mo is working at a small hardware store, and he sells a hammer to Frank. On that day, Mo was alone in the store - if he had not come to work that morning, the store would have been closed. A year later, Frank is messing around during a break at work. He is not paying attention to anyone around him. He swings the hammer around to illustrate a point in a story he is telling, and he accidentally hits a coworker, causing an injury. Which of the following is true of Mo?
a. He is a cause in fact of the injury.
b. He is a proximate cause of the injury.
c. Both A and B.
d. None of the above.