Which of the following could replace ‘pretty well’ as used in the passage?

Directions: Read the following passage carefully and select the most suitable option according to the corresponding number in the passage.

It was October. The pink-white leaves of the flowering dogwood covered (1) the entire yard. The clumps (2) of glossy red fruits, peaping (3) from gaps between its leaves, made the tree look like a giant sundae. A flock of bluebirds flying over the town’s sky couldn’t resist (4) the temptation and nosedived for the tree. The tree looked washed (5) in pink, white and red, with busy blue dots moving all over. The bluebirds were back again. The little six inch birds ate grasshoppers, beetles and caterpillars. But, the fruits of the flowering dogwood surely (6) topped their list of favourites. Their numbers had fallen (7) recently, and may be the starlings and sparrows were giving them a hard time to find nests. But everybody in the town started putting out nesting boxes - and that seems to have worked pretty well (8). The bluebirds have returned to the town.