In which of the following types of contracts is it most important for the contractor to maintain control of cost, schedule and scope changes?

option C is most suitable choice 

yes in the fixed price contract , the contractor must take seriously the control of cost ,shedule and scope changes

Option C (Fixed Bid) - Schedule delays or budget expansion will cause cost escalation, which in turn will eat up the profit margins.

Thanks for invitation....I endorse answers given by colleagues &Experts

C. firm fixed price

In firm fixed price contact, all risk is borne by the contractor. So, the contractor has to control cost, schedule and scope changes in order to make predetermined profit.

Agree with MR  Md. Fazlur Rahman & Mr  Usman Islam 

Answer is 

C. firm fixed price

C. firm fixed price  Is the answer

Obiviously answer has to be C . 

In firm fixed price contract , contractor is supposed to execute the contract successfully in an agreed fixed amount. So contractor has to take care of all the constraints.

In the contract of unit price because in this case because the money that you get depends on the amount of work performed so you have to control your cost in order to make profit while in the other contracts no matter how much the cost is you will be paid the cost plus fees as profit moreover the fees are usually as percentage of the cost so the higher the cost the higher the profit. 

Firm Fixed price, in this contract you need more cost controlling and scheduling.