You are a Contracting Officer for the Department of Agriculture. You need to secure a few vendors for a five- year engagement to, when requested, perform analysis of federal parks' trees and cut down those that are no longer alive. Since you are unsure when the services will be needed or of course how many trees will need to be cut down, you need flexibility. You do have the ability to estimate and establish a ceiling on the number of hours of work and trees that may be taken down. Further, you desire a competitive price each time you request work to be done. Discuss in detail 1) what type of contract you should offer and/or is most suitable and 2) why that chosen contract type is advantageous based on the facts for the government.