The correct answer is expressive.
According to M.H. Abrams, a famous American literary critics, all literary theories can be separated into four groups: mimetic, expressive, rhetorical, and formal.
Mimetic group deals with the relationship between the work itself, and the world surrounding it.
Expressive theories have to do with the connection between the work and the author, which is the case here, since we need to examine the relationship between the poem <em>Introduction to Poetry </em>and its author, Billy Collins.
Rhetorical theories deal with the relationship between the work and the audience reading it, listening to it, or watching it.
And finally, formal theories do the close reading of the work, taking everything into consideration.