Which of the Following Better Explains 'Contract Unit Rate

Which of the following better explains 'Contract Unit Rate'? 

A)  This is a situation where payments are made based upon the contract number of units produced during the completion of the work. 
B)  This is a situation where payments are made based upon the actual number of units produced during the completion of the work. 
C)  This is a situation where payments are made based upon the number of units started during the work. 
D)  This is a situation where payments are made based upon the planned number of units to be produced during the completion of the work.