For which of the cases below do the given functions form a fundamental set of solutions of the corresponding differential equation on the indicased inverval?
(i) y''-15y'+56y=0;6e⁷ˣ,8e⁸ˣ,(-[infinity],[infinity])
(ii) y''-20y'+100y=0;5e¹⁰ˣ,5xe¹⁰ˣ,(-[infinity],[infinity])
(iii) x²y''-12xy'+42y=0;2x⁶,7x⁶,(0,[infinity])

(A) (iii) only
(B) (ii) and (iii) caly
(C) (i) and (ii) only
(D) (ii) only
(E) all of them
(F) (i) only
(G) (i) and (ii) only
(H) none of them