I do believe it is false because you should cross-train. I could be wrong!
I think the problem he is facing is not prioritizing or having a lack of time management. I hope this is correct.
Both does not burn the same amount of calories. Running exert more effort than walking. And that makes running to burn more calories that walking. Not unless you walk more more miles away and run only in a short time.
Thus letter D. is not a true statement
