It’s direct line copy question from PMBOK. See what PMBOK says on this:

Participants in risk identification activities can include the following: project manager, project team members, risk management team (if assigned), customers, subject matter experts from outside the project team, end users, other project managers, stakeholders, and risk management experts. While these personnel are often key participants for risk identification, all project personnel should be encouraged to identify risks.

Since all the project personnel include everyone in the choices given, the question author might have through that way…its correct.

Commercial Break Tip on this –
1. You might not get many such direct questions in real PMP exam. However you will get some! Be prepared for all type of questions.
2. In many questions you will see “Whose primarily duty is to…”. If you see the word “primarily” look for a choice that has wordings for “Project manager and his team”. Keep in mind, for all project phases everyone (all stakeholders) has roles and duty BUT accountability lies to the Project manager and his team.
 

Saket, PMP

Agree with Saket, this type of question will not come in the exam, Project stakeholders will actually include all project personnel., so its just meant to confuse by quoting PMBoK and there is no real value.

Start solving questions only from reputed sources.

Hey Sherif - in real world scenarios project risk is often uncovered by asking what are the barriers that might prevent the project from reaching completion (including business barriers like staff turnover). Each of A, B, and C, would hold only their part of the answer. To be able to holistically answer you would need information from all the project personnel.

SPM Learning, a PMI Registered Education Provider and recepient of the PMI 2010 - Best of the Best award, has a great blog on Risk Management (including a spreadsheet to help identify potential risk and make appropriate plans): http://tiny.cc/buqkgw