Without seeing the specific graph, I can provide guidance based on typical scenarios. If the graph represents rainfall data, the most likely option would be:
The two quantities are the average rainfall in inches and the month of the year.
This choice typically represents how rainfall varies over the months in a year, which is a common relationship depicted in such graphs. If the graph shows data over a different time frame or against another variable, the other options may apply. However, without visual context, this is the most probable answer.