The biggest disappointment has been the absence of any meaningful incentive given to the healthcare sector which can affect the government's agenda of making healthcare affordable and accessible.

The sentence talks about the disappointment caused because of the lack of incentives given to the health sector, which could adversely affect the government's agenda of affordable healthcare. A, B and D fit contextually. They all highlight how the healthcare sector has been neglected by the government. C is incorrect. Any time you express support of a group or the people in it, you're showing solidarity with them. The word is used most often to describe a sense of unity with a political group, a group of striking workers, or people who have been deprived of their rights in some way. It does not fit contextually.