Which substrates will undergo an E2 reaction to give a (Z) alkene?

**What I do know:** E2 reactions are concerted and have an anti-coplanar transition state, where the leaving group and the hydrogen being abstracted have a dihedral angle of 180 degrees.


**What I don't understand**: A does not have a halogen that acts as a leaving group. B has two halogens (bromine and fluorine). Thus, how do I determine the substrate(s), if any, that will undergo E2?


[![enter image description here](https://i.stack.imgur.com/cC2uc.png)](https://i.stack.imgur.com/cC2uc.png)


