Could be better
The problem with this app is that it doesn't take account of the fact that more than one preposition can sometimes go with a word. For example, in its quiz you will be given the word "astonished" and options "at", "in", "with", and "by". Any good dictionary will tell you that "astonished" can go with "at" or "by" interchangeably, but the developers of the app do not seem to be aware of that.