indexed

Surely since body odour is the independent variable it should be on the horizontal axis.

Although body odor -- not in all cases, but often -- is largely dependent on length of time spent on the plane, so is not necessarily the independent variable at all. I'd also add that one's independence can be a factor of a lack of friends, so number of friends is the independent variable.

Jeez, I wonder why everyone is vacating this row?

Since "length of time spent on the plane" and "lack of friends" are not in the graph, body odour is the independent variable.

Maybe friends help you manage body odor...

I have few friends so I can't be sure.

This makes no sense. I'm sure you'll delete this comment. But it just doesnt make sense to me. Degree in statistics and I cant figure the logic out. Sorry. Some of these are good, others not so much.