D lets make it easier suppose you have a circle and a square with the same perimeter which one has bigger sum?circle
[tex]2r\pi = l > > r = \frac{l}{2\pi} > > \pi {r}^{2} = \pi ({ \frac{ {l}^{2} }{4 {\pi}^{2} } }) \\ 4a = l > > a = \frac{l}{4} > > {a}^{2} = \frac{ {l}^{2} }{16 } \\ \frac{ {l}^{2} }{4\pi} > \frac{ {l}^{2} }{16} [/tex]
so D has the biggest surface
