Answer
B
Work Step by Step
We first write the equation in the form $y=a \cos [b(x-d)]$. Therefore, $y=3\sin (2x-4)$ becomes $y=3\sin [2(x-2)]$.
Comparing the two equations, $a=3,b=2$ and $d=2$.
The amplitude is $|a|=|3|=3.$
The period is $\frac{2\pi}{b}=\frac{2\pi}{2}=\pi$.
The phase shift is $|d|=|2|=2.$
Therefore, the description in option B is the correct answer.