The subject of the last paragraph is option B) The intense colors of the birds.
Explanation:
The writer names several kinds of birds and makes comparisons between their colors and the colors of different flowers to give a more vivid image. For example "The jays are bluer than the calamus bed they wrangle above with throaty chatter."
"The ripest spray of goldenrod is not so highly coloured as the burnished gold on the breast of the oriole that rocks on it."
