Hello there!
The kind of grain the Robinson Crusoe grow was mainly actually barley. Barley is known to be a cereal wheat kind of food, and back then in Crusoe kind of climate, it was very simple to plant this kind of food, based from the climate and the quality of his soil that Robinson has been taking care of.
A. corn
B. wheat
C. barley
D. rye
I hope this helps you!