(d)
LHL$= \lim_{x \rightarrow 1^{-}}f(x) = \lim_{h \rightarrow 0}1 - h + a = 1 + a$
RHL$= \lim_{x \rightarrow 1^{+}}f(x) = \lim_{h \rightarrow 0}3 - (1 + h)^{2} = 2$
For $f(x)$ to be continuous, LHL=RHL
$\Rightarrow 1 + a = 2\ \ \ \ \Rightarrow \ \ \ a = 1$