Let \([\cdot]\) denote greatest integer function. If \(f(x)=[x]\) and \(g(x)=3\left[\frac{x}{3}\right]\), then the set of all real x such that f(x) = g(x) is
1
\(\mathbb{R}\)
2
\(\left\{{x\in\mathbb{R}/x=3k,k\in \mathbb{Z}}\right\}\)
3
\(\left\{{x\in\mathbb{R}/3k-1< x \leq3k,k\in \mathbb{Z}}\right\}\)
4
\(\left\{{x\in\mathbb{R}/3k\leq x<3k+1,k\in \mathbb{Z}}\right\}\)