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Mathias was asked whether the following equation is an identity:$\newline$$$2 x^{2}+10 x+6=(x+3)(2 x+1)+3(x+1)$$$\newline$He performed the following steps:$\newline$$$2 x^{2}+10 x+6$$$\newline$$\stackrel{\text { Step } 1}{\hookrightarrow}=2 x^{2}+7 x+3+(3 x+3)$$\newline$$\stackrel{\text { Step } 2}{\hookrightarrow}=2 x^{2}+6 x+x+3+3(x+1)$$\newline$$\stackrel{\text { Step } 3}{\hookrightarrow}=2 x(x+3)+(x+3)+3(x+1)$$\newline$$\stackrel{\text { Step } 4}{\hookrightarrow}=(x+3)(2 x+1)+3(x+1)$$\newline$For this reason, Mathias stated that the equation is a true identity.$\newline$Is Mathias correct? If not, in which step did he make a mistake?$\newline$Choose $1$ answer:$\newline$(A) Mathias is correct.$\newline$(B) Mathias is incorrect. He made a mistake in step $1$.$\newline$(C) Mathias is incorrect. He made a mistake in step $3$.$\newline$(D) Mathias is incorrect. He made a mistake in step $4$.