A. A little mouse may even help a lion.
B. Even a little mouse may help a lion.
C. A little mouse can even help a lion.
D. Even a little mouse ought to help a lion.
The given sentence contains one of Model verb (Model Verb = will, shall, can, may, might, could, might, must, would). It is in passive voice.
Rule :
Subject + Model verb + V1 + Other agents