Ans: B
Note that $y=a\cos(2x^\circ + 120^\circ)+b$ means contracting the graph to $\dfrac{1}{2}$ along $x$-axis and then translating the graph $120^\circ$ to the left, and then enlarging the graph $a$ times along $y$-axis, and lastly translating the graph $b$ units upwards.
Note that $y=a\cos(2x^\circ + 120^\circ)+b$ means contracting the graph to $\dfrac{1}{2}$ along $x$-axis and then translating the graph $120^\circ$ to the left, and then enlarging the graph $a$ times along $y$-axis, and lastly translating the graph $b$ units upwards.
By comparing the graph of $y=\cos x^\circ$, we have $a=2$ and $b=2$.
