According to * * * point force balance conditions, there are
FAB=2mg？ Cos30 = 3 mg
FCD = 2 mg? sin30 =mg
Then analyze the force of C ball, as shown in the figure.
According to * * * point force balance conditions, there are
X direction: fcdcos 30-fbccos α = 0.
Y direction: fcdsin 30+fbcsin α-mg = 0.
solve
FBC = mg
α=30
So choose ABC ..