How does the gradual shortening of lines most clearly contribute to the
meaning of the poem?

the correct answer is the last option

hope this

your pal abigail

the answer is

  this riddles' answer is library.

  the "leaves" are a reference to the books' pages that the library contains; the branches are a network of libraries that connect multiple libraries' collections, resources, and items in a system of a common database, integrating them; the branches' organization are a useful management tool for coordinating the multiple collections many libraries have.