I would like to know the answer please

Ithink the answer is pollution in the air steel made of iron and carbon

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

What are the options? physical property can be color, smell, opacity, viscosity, density, infra red spectrum, melting and boiling points, attraction and repulson to magnets, etc.

Answerspecies;