Answer:
The correct option is that the expected or the average cost of all the weekly rat purchases is $13.
Step-by-step explanation:
Option a is true as there is no definite information about the future pricing is indicated. However from the historic data, it can be stated that the expected or average cost for all weekly rat purchases is $13.
Option b is not true as the statement given is a definition of mode of the purchase. There is no such information in the question.
Option c is not true as there is no information in the question indicating that the purchases are evenly distributed below and above the value of $13.
Option d is not true as there is no indication of this occurrence in the question in the definitive way.