The correct answer is: A. work certified.
The basis for the payment of cash by contractee under contract is work certified. This means that the contractor is paid for the work that has been completed and certified by the owner or the engineer. The work is certified after it has been inspected and found to be in accordance with the contract specifications.
Option B, work uncertified, is incorrect because the contractor is not paid for work that has not been completed or certified. Option C, contract cost, is incorrect because the contract cost is the total amount of money that the contractor is entitled to be paid, not the basis for the payment of cash. Option D, value of plant used in the contract, is incorrect because the value of the plant used in the contract is not a factor in the determination of the amount of money that the contractor is paid.