Ok, here we have this, for f(x)=A*g(Bx-C)+D, where g(x) is one of the trigonometric basic functions, C/B is called a phase shift, so if we work, we get this:
2cos(3x+2pi)+1
f(x)=2cos(3x+2pi)+1
g(Bx-C)=cos(3x+2pi), B=3, C=-2pi, D=1
Then, the phase shift is: C/B= -2PI/3
So, the correct answer is D.
