The Food Chain

Plant (producer) → Insect (herbivore) → [M] (primary carnivore) → Snake (secondary carnivore) → Eagle (top carnivore)

The missing link M must be:

• An organism that eats insects (making it insectivorous)
• And is itself preyed upon by snakes

(A) Rabbit - incorrect (herbivore, doesn't eat insects)
(B) Wolf - incorrect (higher carnivore, wouldn't be eaten by snakes)
(C) Frog - correct (insectivorous and preyed upon by snakes)
(D) Ichthyophis - incorrect (a legless amphibian that snakes wouldn't typically eat)

Thus, the complete chain is:
Plant → Insect → Frog → Snake → Eagle