12. Singletons are most useful for:a.Not having to create many instances of the same class, e.g. instance of a null object.b.Keeping a class’s API cleaner.c.Keeping track of global state.d.Decreasing global variables clutter, because we can use singletons to replacing anyglobal variables e.g. $variablewe would have created.
13. Where is the best place to store a runtime feature flag on/off value.
14. With continuous integration, what is the best way to hide a large incomplete feature fromusers? This feature is being worked on by 10 engineers and will span multiple iterations. Wedo not want to leak the feature to user's browsers until ready for launch.
15. Unit tests should:
16. Select ALL that apply. Examples of a proxy object include:a.A DirectionsServicethat serves cached offline results if the user has downloadedthis city's map area, else calls the Maps server.b.A MailServicethat sends out the email if online, else queues the email for sending.c.Movies.reviews, which returns an object that acts like a Collection of DB dataobjects, but doesn't actually do the SQL query until you need to.d.The subclass CanadianGoose, that subclasses Goose, and overrides the superclass'drawmethod to output a different PNG image.
17. Which is FALSE about the observer pattern: