We form associations between two occurrences when

We form associations between two occurrences when they occur at the same time very often. 

For example, if it happens regularly (but by coincidence) that someone gets sick if a distant relative visits, people might start linking those events and believe that there is an correlation between them, or even a causation. 

This is often how superstitions arise. 

Reflects an exhaustive study of it's words.

Ibelieve that it is..d) fall.