Eleven letters are shared by the Greek, Latin and Russian Cyrillic alphabets (if you consider Y / У and K / К to be the same). In this dandy Venn diagram, the set of Greek upper-case graphemes is on the left and the set of Russian Cyrillic is on the bottom.

What could you say, in English, with only the letters common to all three alphabets, and using each letter only once?

Boxy kept ham.
Ham kept by ox?
Oh! Kept by Max.

Hob kept my ax.
Ax kept by Ohm.
Both make pyx.

Ah. Kept my box.
Ha! Kept my box.
Bah! Kept my ox.

∞