This is a sentence written in present tense (indicative mood) with the 3rd person in plural ellas (they), which are las serpientes (the snakes).
Now the verb preferir (to prefer) is conjugated under these conditions explained above as prefieren (they prefer).
Therefore the complete sentence is:
Snakes prefer to eat mice
The other options are incorrect because:
-Priefere does not exist as a word in spanish
-Preferen does not exist as a word in spanish
-Prefiere (prefer) although is in present tense indicative, is conjugated with the 3rd person in singular, therefore it does not match with the subject of the sentence
