you can not create an instance of IMessagingService, it was declared as an interface. Since EmailService inherits the IMessagingService interface the private member variable can hold an instance of an EmailService. Interfaces are a contract for other classes to fullfill through inheritance they do not contain concrete code and can't be instantiated.
You can easily check out our high quality Pass4sure 70-461
which prepares you well for the real network+ practice questions
You can also get success in real hodges
exam with the quality University of Saint Joseph