Forced choices or forced alternatives are a good way of prompting. Simply it means, giving the client two options to choose the right one from when he is unable to respond appropriately.
Here is an example:
If you are showing a picture of a girl who is crying to your client and asking what the girl is doing, you can cue her by giving options " Is she crying or eating? " ( more distractive and child finds easy to choose from) or " Is she crying or carrying?" ( difficult to choose because phonemically similar) when she is unable to answer independently,
I identified some problems using forced choices in prompting. According to my experiences, forced choices are less effective for the kids who have echolalic features. They more tend to repeat the whole forced choices instead of choosing the right answer.
eg. ST: Is she eating or crying?
Child: eating or crying
For the kids like that, prompting with phonemic cues ( eg. K..for crying) are more effective.
However you can try forced choices with kids with speech and language delays successfully.