For the function $f(x)=2x^3-6x^2+6x+5$, the point $x=1$ is

1. $f'(x)=6x^2-12x+6=6(x-1)^2$. 2. $f'(x)=0$ at $x=1$, so it is a critical point (D wrong). 3. $f'(x)\ge 0$ everywhere and does not change sign through $x=1$. 4. By the first derivative test, $x=1$ is neither maxima nor minima; it is a point of inflexion. _Source: syllabus Mathematics Ch 6 "Application of Derivatives", p.19_