You should have an array, INI, or hashtable of the correct answers. More specifically, the key words for the answer. Then when the user inputs their text and clicks the button you then parse the input text and check the text against your stored right answer.
For example, for the question, "What is the longest river in the world?" The answer, Nile will be stored in some type of data structure mentioned previously that is indexed to the question. When the user types their answer, use the text manipulator object to grab each input text and compare to "Nile". That way answers like, "the Nile" will be correct as well.
You can also do this with Python and regular expressions but I think you might be able to get by fine with just Construct objects.
Edit: Oh.. for math then just compare the integers etc...