Norder for a double replacement reaction to take place, the reactants must be

The reactants and products must be both compounds.

Ex. AB+CD --> AD+BC

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later

The answer is b because c don't explain why the moths are on them and it isn't a because as we know only one species of moth does this