Simplify ratio 1.5:2.5

If 2(a^2+b^2)=(a+b)^2 then, > a+b=0, > ab=0, > a=b, > 2a=b

Which of the following is the major negative aspect of crossover designs for research studies? a. prohibitive cost b. residual effects c-subject drepout d. incomplete randomization e. large sample size required

Which answer choice is it? is it the first ,second,third or fourth giving 40 points for whoever answers correctly you