The Model Selection dialog can be used to view the models that have been activated in a continuum.
As shown below, the Optional Models group box on the left-hand side of the dialog lists the models that have not been selected, but are not necessary to complete the continuum. These models would only be selected if you determined that they were warranted by the physics of the situation.
The Enabled Models group box on the right-hand side of the dialog shows all the models that have been enabled. The selections that are grayed out may not be disabled, since they are required by other (non-grayed-out) models. Therefore, the non-grayed-out models will have to be de-selected first.