What does Event Series Join do?

A.
enables analysis of two series of data when their measurement intervals do not align

B.
evaluates the values of a given set of variables and groups those values into a window

C.
enables identification of a sequence of defined events

D.
increments a counter based on whether an expression evaluates as true

Explanation:
http://www.vertica.com/wp-content/uploads/2011/06/Whats-New-in-Vertica-50.pdf
(page 1, see event series join)