Most Trips Taken Abroad by Members of Congress Are Bipartisan

Most trips taken abroad by members of Congress are bipartisan. What does the trendline for the bipartisan nature of these trips tell us?

A) More bipartisan trips occur each year
B) An increasing number of trips are partisan
C) About the same number of trips have been bipartisan for the last decade
D) The number of bipartisan trips used to be extremely low, but trips have become much more bipartisan in recent years