Okay, I have a slight hunch about what story this is (To Build a Fire by Jack London?) and if so, then D
Explanation:
Because McDonald's is the second largest chain of fast food around the world. There are around 36,000 outlets worldwide. People are so in love with McDonald's and so crazy about it that people started to eat as their meal everyday. So Morgan Spurlock wanted to show what could happen if kept living on McDonald's.
Therefore implies that something is occurring as a result of something else. As a result, therefore best implies a cause and effect structure.
they clean all areas to stop the spread of any infections
