Let $f:\left(-\infty ,\infty \right)\overrightarrow{0,\infty }$ be a continuous function such that $f\left(x+y\right)=f\left(x\right)+f\left(y\right)+f\left(x\right)f\left(y\right),\forall x\in R\dot{}$ Also $f^{\prime }\left(0\right)=1.$ Then $\left[f\left(2\right)\right]$ equal \displaystyle{\left({\left[{\dot}\right]}\right.} represents the greatest integer function$)$$5$ b. $6$ c. $7$ d. $8$

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