How many solutions are there to (1+3cos3θ)2=4(1+3\cos3\theta)^2=4(1+3cos3θ)2=4 in the interval 0∘≤θ≤180∘0^\circ\le\theta\le180^\circ0∘≤θ≤180∘? A111B222C333D444E555F666