why not C) ?
1) t/u * t-u > 0 => (t(t-u))/u > 0 => t(t-u) > 0 or t(t-u) < 0 => insuffcient
2) t^2/u^3 > 0 => insufficient but u must be +ve
1)+2) u is +ve so => t(t-u) > 0 => t>0 or t>u.we know from 2) that u is +ve so u * t is +ve.
correct me if i am wrong. thx.
If your mind can conceive it and your heart can believe it, have faith that you can achieve it.