27. Let $f$ be twice differentiable function satisfying $f ( 1 ) = 1 , f ( 2 ) = 4 , f ( 3 ) = 9$, then :\\
(a) $f ^ { \prime } ( x ) = 2 , \forall x \hat { I } ( R )$\\
(b) $f ^ { \prime } ( x ) = 5 = f ^ { \prime \prime } ( x )$, for some $x \hat { I } ( 1,3 )$\\
(c) There exists at least one $x \hat { I } ( 1,3 )$ such that $f ^ { \prime } ( x ) = 2$\\
(d) none of these\\