Ans: A
$\begin{array}{cl}
& f(5)-f(3) \\
= & (5)^2+2(5) +k – [(3)^2+3(3)+k] \\
= & 35 + k – 15 – k \\
= & 20
\end{array}$
$\begin{array}{cl}
& f(5)-f(3) \\
= & (5)^2+2(5) +k – [(3)^2+3(3)+k] \\
= & 35 + k – 15 – k \\
= & 20
\end{array}$
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