D. myFooController m = new myFooController();System.assert(m.prop ==null);

Here’s the reasoning:

The class myFooController is defined with a public integer property prop that has a getter but a private setter. This means that the prop property can only be modified within the class and not outside of it.

When a new instance of myFooController is created, prop is not initialized to any value explicitly within the constructor (assuming the default constructor is used since none is defined in the provided code). In Salesforce Apex, uninitialized primitive properties (including Integer) default to null. Therefore, immediately after creating a new instance of myFooController, the value of prop will be null.

Hence, the assertion System.assert(m.prop == null); will be true, making option D correct.