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Alaina was asked whether the following equation is an identity:$\newline$$$(2 x+1)^{2}-(x+1)^{2}=3(x+1)^{2}-1$$$\newline$She performed the following steps:$\newline$$$(2 x+1)^{2}-(x+1)^{2}$$$\newline$$\stackrel{\text { Step } 1}{\hookrightarrow}=4 x^{2}+4 x+1-x^{2}+2 x+1$$\newline$$\stackrel{\text { Step } 2}{\hookrightarrow}=3 x^{2}+6 x+2$$\newline$$\stackrel{\text { Step } 3}{\hookrightarrow}=3 x^{2}+6 x+3-1$$\newline$$\stackrel{\text { Step } 4}{\hookrightarrow}=3\left(x^{2}+2 x+1\right)-1$$\newline$$\stackrel{\text { Step } 5}{\hookrightarrow}=3(x+1)^{2}-1$$\newline$For this reason, Alaina stated that the equation is a true identity.$\newline$Is Alaina correct? If not, in which step did she make a mistake?$\newline$Choose $1$ answer:$\newline$(A) Alaina is correct.$\newline$(B) Alaina is incorrect. She made a mistake in step $1$.$\newline$(C) Alaina is incorrect. She made a mistake in step $3$.$\newline$(D) Alaina is incorrect. She made a mistake in step $5$.