According to the Scrum Guide, the Sprint Review is a time for the Scrum Team and the stakeholders to inspect the product Increment and adapt the Product Backlog if needed. The Product Owner is responsible for keeping the stakeholders aware of the progress of the project and inviting them to the Sprint Review. If the Product Owner has not been doing this, or if the stakeholders have not been using the Sprint Review to inspect and evaluate progress, then they may be disappointed and angry at the seventh Sprint Review. The other options are not likely factors that led to this situation, as they are either irrelevant (such as the PMO or the development area) or incorrect (such as delaying the release).