There Can Be No Contract Where

There can be no contract where:

A) The contract states that the prices and the dates of payment are to be agreed upon from time to time by the parties.
B) The contract makes no mention of the price or date of payment.
C) The contract specifies that the buyer is to fix the price at a future date.
D) The contract states that the price is to be agreed by two valuers, nominated by the parties, and in default of such agreement, by an umpire appointed by the valuers.