Evidence and details from the text
The correct answer should beThrough primrose-tufts, in that sweet bower,The periwinkle trail’d its wreathes;
Alliteration is when words in the same sentence begin with the same consonant and here we have "through, tufts, the, that, trail'd" as well as "primrose, periwinkle".
He is referring to the bird as clumsy because "ungainly" is define as "awkward" or "clumsy" and "fowl" is another word for "bird"
I believe it is C. Slippy because it basically means to fall