In Carl Sandburg's poem "Grass" readers know that speaker cannot be the author because the speaker is the grass, as expressed in option D and explained below.
Simply put, we can say the speaker of a poem is the imaginary or real person saying the things in the poem. However, the speaker is not necessarily the author of the poem.
That is the case with the poem "Grass." The author is Carl Sandburg, but the speaker is the grass itself. The poem is basically the grass talking about covering dead bodies after bloody wars have taken place.
With the information above in mind, we can select option D as the correct answer.
Learn more about speakers here:
https://brainly.com/question/17543484