You create a model-driven app. There is a subgrid Reviews on the Information screen for the Product record. You need to open an alert dialog when a user clicks on the "Great performance" review. You want to use a JavaScript code that implements a Client API model. Here is the line from your Javascript code with access to the subgrid: 

What is the type of Client API Context object is the SLOT1?

Answer options:

A.Xrm
B.gridContext
C.formContext
D.executionContext

Correct Answer: C 
Power Apps provides the Client API model for model-driven apps for users to implement for their business logic. The Client API model includes objects and methods that developers can access using Javascript code. 
There are four root objects of the Client API model: executionContext — this is an execution object of the model-driven app. It gives access to the context of the forms and grids.
formContext — provides access to the form object using the executionContext.
gridContext — provides access to the grid (subgrid) on a form.
Xrm — provides access to the global object for operations that do not directly impact UI and data in forms, grids, controls.
Here is the sample of the Javascript implementation of the task: 

The executionContext provides access to the formContext object (Number 1). The formContext gives access to the gridContext object (reviewsContext) (Number 2). And Xrm opens the Alert Dialog form (Number 3). 
For more information about model-driven apps Client API model, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/understand-clientapi-object-model
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/clientapi-grid-context