Giving a part of project work to a contractor is an example of:

Risk assumption (acceptance) means the project team acknowledges the risk and decides not to change the project plan to deal with it, rather than shifting it to another party.

Risk assignment is not a standard PMI risk response strategy; the recognized term for shifting risk to an outside party is transference or deflection.

Risk delegation is not a recognized PMI risk response strategy; delegating work internally does not transfer risk to an outside party.

Risk deflection (also called risk transference) shifts the negative impact of a risk and ownership of the response to a third party such as a contractor or insurer. When project work is outsourced to a contractor, the contractor assumes the risk associated with performing that work, effectively deflecting the risk away from the buyer's project team.

Risk mitigation involves reducing the probability or impact of a risk, not transferring it to another party through a contract or outsourcing arrangement.