Let $f(x)=x^2+3x.$ Which of the following is equal to $f^{\text{'}}(x)?$

$($A$)\underset{h0}{lim}\frac{x^2+3x+h-x^2-3x}{h}$

$($B$)\underset{h0}{lim}\frac{(x+h{)}^2+3x-x^2-3x}{h}$

$($C$)\underset{h0}{lim}\frac{(x+h{)}^2+3(x+h)-x^2-3x}{h}$

$($D$)\underset{h0}{lim}\frac{(x+h{)}^2+2x-x^2-2x}{h}$

$($E$)\underset{h0}{lim}\frac{(x+h{)}^2+3(x+h)-x^2+3x}{h}$