How can I respond if I have 20 days to answer court for foreclosure but I am in review of loan modification with the lender?

You respond by admitting, denying, or saying that you are without knowledge as to the separate numbered paragraphs in the complaint, and then by setting up affirmative defenses that you have. You need an attorney on your side to do this because you know nothing of affirmative defenses that might be available to you. There has been much case law in the past few years from which you might be able to get some valid affirmative defenses.