Statement (A) : For cis - isomer $\mu \ne 0$.

Statement (B) : Generally for trans isomer $\mu =0$.

Statement (C) : For ${\text{BF}}_3$ molecule $\mu =0$.

Cis-isomer ($\mu \ne 0$) and trans isomer ($\mu =0$ ) can be distinguished one from another with the help of dipole moment.  In cis-isomer, both dipoles are in same direction. Hence, the resultant dipole moment will not zero, $\mu \ne 0$. But in trans isomer, both dipoles are in opposite direction in equal amounts. So, the resultant dipole moment of a molecule is $\mu =0$.

                         Cis form ($\mu \ne 0$ )                   trans form ($\mu =0$ )

In ${\text{BF}}_3$molecule, the dipole moment of one B-F bond should be equal and opposite direction to the dipole moment of remaining two B-F bonds. Therefore, the resultant dipole moment of  ${\text{BF}}_3$ molecule is $\mu =0$.