What does the "lock and key" model refer to?

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.

some fungi obtain their nutrients from a living host (plant or animal) and are called most biotrophic fungi have fairly narrow host ranges—they are specialized on a limited called rhizomorphs that allow the fungus to grow from one tree to another. ascospores are formed inside a sac-like structure called an ascus. so your answer is a