Answer:
A: how much grain was produced
Step-by-step explanation:
The Y axis of a graph is represented by the line that is vertical. In the graph shown in the figure above, the Y axis is the one with the title "Millions of Tons."
The title of the graph shows that the graph seeks to present grain production in China. So, if the Y axis represents the millions of tons produced over the years, we can see that the Y axis refers to the amount of grain produced in China, in different years, so the answer to your question is the letter A.