"A" is correct because in the case of browser based HTML clients (thin clients), information CANNOT be pushed without client polling i.e. without client making a GET / POST request. Usually browser based client
is PULL System, meaning clients request information from the server. In the other case of thick clients, say
applets, server can PUSH data to the Rich Client based on state changes in the model. In the latter case,
applets or rich clients didn't make a request for info, but yet server data gets PUSHED. This is usually done using the technique similar to observer
pattern.
model.registerObserver(view) ---- This would cause the view to be updated when the model changes internally.
I think D is correct because in the case of, say AJAX based rich clients, server can send incremental data using JSON to update just a grid in the UI upon client requests without fully reloading the page. Whereas with HTML,
the entire page may need to be reloaded