For each of the following, decide whether there has been a valid offer:

A . “Would you like to buy my cabin in Maine? It’s a beautiful piece of lakefront property and could sell for more than \($500,000\) if I used a real estate broker to sell it.”
B. “I’m looking to make some extra money over summer vacation. I’ll paint the exterior of your house, two coats, nice job, if you’ll pay me \($20\) an hour.”
C. “I know it’s only June, but I’m expecting a crop of McIntosh apples in October and can sell you 10 bushels at \($70\) per bushel.”
D. “I will be able to mow your lawn for \($50\) as soon as possible.”
E. A contractor and a homeowner agree that the contractor will build a house according to certain specifications and plans, drawn and approved by an architect, for a stated price. The homeowner will be given a range of choices for appliances, interior and exterior paint colors, and carpet, but the homeowner has not yet selected these.
F. “Some of the coins in my collection are pretty rare. Maybe you’d be interested in the older ones?”