what is the main reason other members of the EU are concerned about the British decision to leave the EU?

a. they are concerned that other nations will want to leave the EU after Britain
b. they are concerned that English will not be spoken in the EU any longer
c. they are concerned that Britain will join competing economic unions
d. they are concerned that Britain will no longer trade with EU nations

a. they are concerned that other nations will want to leave the EU after Britain