Which of the Following Would Be an Offer (And Not

Which of the following would be an offer (and not an invitation to treat) ?

A) An auctioneer advertises that she will sell goods without reserve, and those goods are put up for sale.
B) A shop owner displays goods in a shop window.
C) An invitation to tender, asking for tenders for the supply of certain goods.
D) An auctioneer puts up certain goods for sale.