Referring to the Class Scenario, CS&F $($Uncle Jims$)$ are improving the way that they purchase sugar. Which ONE of the following is the BEST example of a pull system?

Select one:

a$.$ CS&F sign a framework agreement with a selected supplier for a regular quantity of sugar to be delivered every two days. Because of the regular small order the supplier can afford to invest in a smaller delivery vehicle so both sides save money

b$.$ CS&F sign a framework agreement with a selected supplier agreeing a discount of the open market price of sugar. When the factory gets low on sugar the CS&F purchasing department sends in an order to the supplier for $10$ tons

c$.$ CS&F sign a framework agreement with a selected supplier. The selected supplier monitors the price of sugar and when the price is forecast to rise quickly orders $6$ months$$ supply on behalf of CS&F

d$.$ CS&F sign a framework agreement with a selected supplier for a regular quantity of sugar to be delivered every three months at a fixed price

e$.$ CS&F sign a framework agreement with a selected supplier such that when sugar supplies drop to a pre$-$determined level CS&F send in a $$top$-$up$$ order to the supplier to bring levels up to a previously established level