Right choice is (c) contingency
Explanation: When using an estimate which has no contingency to set a budget or to set aside funding, a contingency is often added to improve the probability that the budget or funding will be adequate to complete the project. Being unable to complete a project risks public ridicule. See cost contingency for more information. The estimate or budget contingency is not intended to compensate for poor estimate quality, and is not intended to fund design growth, owner changes, or anything else unrelated to delivering the scope as defined in the estimate documentation. Generally more contingency is needed for earlier estimates due to the higher uncertainty of estimate accuracy.