 
 <translate> Another way: Any letter (x, y, z, w) can be included or not. So, we have 2^4 combinations - 4 empty combination = 12 combinations
The final answer: (B). <ibo> Ụzọ ọzọ: A pụrụ ịgụnye mkpụrụ akwụkwọ ọ bụla (x, y, z, w) ma ọ bụ ghara ịgụnye ya. Ya mere, anyị nwere 2 n'ike nke 4 jikọtara - 4 oghere jikọtara = 12 jikọtara Azịza ya bụ: (B). 