Answer:
Mary
Step-by-step explanation:
Mary has a competitive advantage and has a lower opportunity cost than Bill just having to sacrifice 2 units of food for 1 shelter, while Bill has to sacrifice 4 units of food for producing 1 unit of shelter. It is possible to observe this in the production relation:
Mary's productivity:
![(1)/(2)=0.5](https://img.qammunity.org/2020/formulas/mathematics/middle-school/nw6stzxu30t062jkvh7ucpfuled611foa0.png)
Bill's productivity:
![(1)/(4)=0.25](https://img.qammunity.org/2020/formulas/health/high-school/r82nicixgizumw833cll8nrqalm6mu5mdg.png)
We see that Mary has a higher productivity rate, which means that she has the competitive advantage