First look and see if each of the values are true (attainable) before looking at efficiency
A.Producing 0 chocolate bars and 100 cans of cola is both attainable and efficient.
This is attainable
B.Producing 20 chocolate bars and 80 cans of cola is attainable but inefficient
This is not attainable
C.Producing 30 chocolate bars and 38 cans of cola is both attainable, with an inefficient
This is attainable
D.Producing 40 chocolate bars and 0 cans of cola is both attainable and inefficient
This is attainable
Now lets looks at efficiency
efficient when it is producing at the lowest point on the graph
Inefficient is below the graph
D should be efficient
A should be efficient
I am not sure why C is wrong