I am doing a biology science fair. Here is my plan: I am going to ask my pharmacist for HCG containing pills, and put them into 5 different cups - one which will remain as a constant I can compare the others to. To the other four, I will add different chemicals, then test them for HCG using pregnancy tests. I need to know what I should research. I already obviously know I need to research how pregnancy tests work, and about HCG. Is there anything else I am missing that might be significant? More importantly however, I need to know which chemicals I should add so that they can somewhat alter the results. Please help me out, this is my first time doing a science fair.