You just chose the right answer. If you look at the general reaction:

2 M + n RX ----> RM + MX   If metal is in group I of the periodic table.
                             or RMX    If metal is from group II to IV of the periodic table.

Beryllium is an element of group II so will lead to: R_xMX_y
(x+y = n the groupperiodic table)

Now go on with the next problem.

Go to next question.