According to the theory of evolution, birds’ feathers evolved from _______. (a) gill slits. (b) reptile scales. (c) fish fins. (d) gill arches.

The correct answer is (b) reptile scales. Birds are believed to have evolved from small, feathered dinosaurs. These dinosaurs likely had simple, downy feathers that evolved from modified reptile scales. Over time, feathers became more complex and specialized for various functions such as flight, insulation, and display. Today, birds have a variety of feather types that serve different purposes, but they all share a common evolutionary origin from reptile scales.