Which of the following is buyer-prepared formal request sent to seller and is basis upon which seller prepares n bid?

I understand from your question that.  what the seller action when he receive a formal request to go in a bid. 

When buyer ask seller by a formal request. 

The seller will replay by an offer with full package " specification , price , time for delivery , payment condition  , ........ , ..... ".  And may be  replay with a proposals If he had more choices for buyer. 

In the other side. 

If we took a look for your choices. 

A. Contract. It will made after acceptance From both sides.  

B. Procurement  request. It made by buyer asking from seller. " formal request "

D. Procurement doucument package. It made by buyer. 

E. Proposals. It made by seller to cover all needs from buyer. 

Hope that  I get the answer that you need. 

Thank you. 

Answer: D

D. Procurement document package