Explanation:

The correct answer is option 'A' - Grasshopper.

In the poem "The Poetry of Earth" by John Keats, the speaker describes the various sounds of nature that can be heard during the summer season. The poem personifies these sounds as different creatures, and one of them is the grasshopper.

Here is a detailed explanation of each option:

a) Grasshopper:
- The grasshopper is known for its unique chirping sound, which is often associated with summertime.
- In the poem, the grasshopper is described as "singing" its song.
- The speaker refers to the grasshopper's song as the "poetry of earth" in the summer season.

b) Cricket:
- While crickets also make a chirping sound, they are not mentioned in the poem.
- The poem specifically mentions the grasshopper as the creature that sings the poetry of earth.

c) Crowd:
- The term "crowd" does not refer to a specific creature or sound associated with nature.
- It is not mentioned in the poem as the source of the "poetry of earth."

d) Skylark:
- The skylark is known for its melodious song, but it is not mentioned in the poem.
- The poem focuses on the sounds of creatures found on the ground, rather than those in the sky.

In conclusion, the grasshopper is the creature that sings the poetry of earth in the summer season, according to the poem "The Poetry of Earth" by John Keats.