The correct answer is: C. percentage of work certified as done.
The percentage of work certified as done is the basis for determining profit to be taken into account on incomplete contract. This is because the percentage of work certified as done represents the amount of work that has been completed and is therefore the amount of work for which the contractor is entitled to be paid.
The cost of contract is not the basis for determining profit to be taken into account on incomplete contract because the cost of contract does not represent the amount of work that has been completed. The contract price is also not the basis for determining profit to be taken into account on incomplete contract because the contract price is the amount that the contractor is entitled to be paid for the entire contract, not just the amount of work that has been completed. Uncertified work is also not the basis for determining profit to be taken into account on incomplete contract because uncertified work is work that has not been completed and is therefore not work for which the contractor is entitled to be paid.