Which of the Following Best Explains a 'Request for Proposal

Which of the following best explains a 'Request for Proposal (RFP) '? 

A)  Suppliers are invited to submit a final proposal after the buyer's invitation to tender which meets the requirements as laid down in the request for quotation. 
B)  Suppliers are invited to submit a first proposal prior to the buyer's invitation to tender which meets the requirements as laid down in the request for quotation. 
C)  Suppliers are invited to submit a first proposal after the buyer's invitation to tender which meets the requirements as laid down in the request for quotation. 
D)  Suppliers are invited to submit a final proposal prior to the buyer's invitation to tender which meets the requirements as laid down in the request for quotation.