Riddle

Only two backbones and thousands of ribs.

Choose an answer

A.Xylophone
B.Zipper
C.Ladder
D.Railroad
Hint: It's a word with 8 letters, starting with "R".

Answer

Railroad

Why this is the answer

A railroad's two parallel rails act like 'backbones,' while the many wooden crossties resemble ribs.

This riddle is filed under Hard/Difficult Riddles and rated Medium.