The project manager should implement the risk handling strategies for the risks that occur more frequently, as this will help reduce their impact on the project and improve overall project performance.
Exploit is a positive risk response strategy that aims to ensure that the opportunity is realized 1. It involves eliminating the uncertainty associated with a particular upside risk and making it happen 2. For example, if there is an opportunity to reduce the project cost by using a cheaper supplier, the project manager can exploit it by signing a contract with the supplier and securing the savings. Exploit is the opposite of avoid, which is a negative risk response strategy that seeks to eliminate the threat or protect the project from its impact 2.
The other options are not appropriate for taking full advantage of opportunities. Mitigate is a negative risk response strategy that reduces the probability and/or impact of a threat 2. It is the opposite of enhance, which is a positive risk response strategy that increases the probability and/or impact of an opportunity 1. Accept is a risk response strategy that involves acknowledging the risk and not taking any action unless the risk occurs 2.
It can be applied to both threats and opportunities, but it does not actively pursue them. Transfer is a negative risk response strategy that shifts the impact of a threat to a third party, along with ownership of the response 2. It is the opposite of share, which is a positive risk response strategy that allocates ownership of an opportunity to a third party who is best able to capture it for the benefit of the project 1.
References: 1: How To Exploit and Enhance Project Opportunities - Project Risk Coach 2 2: A Guide to the Project Management Body of Knowledge (PMBOKGuide) - Sixth Edition, page 443-4451