A plant will recognize a pathogenic invader A) if it has many ...

[xclash]

A plant will recognize a pathogenic invader
A) if it has many specific plant disease resistance (R) genes.
B) when the pathogen has an R gene complementary to the plant's antivirulence (Avr) gene.
C) only if the pathogen and the plant have the same R genes.
D) if it has the specific R gene that corresponds to the pathogen molecule encoded by an Avr gene.
E) when the pathogen secretes Avr protein.

[clippers!]

I chose D and got the answer, hope that helps.