In the context of the passage from Susan Glaspell's "Trifles," the correct answer for an example of external motivation is:
C. The bird is found because Mrs. Peters and Mrs. Hale were looking for sewing things.
This choice illustrates how the characters' actions—specifically their search for items to take to Mrs. Wright—lead them to discover the dead bird, which is a pivotal moment in the play. Their intent to find sewing supplies is the external motivation that drives their discovery, which ultimately deepens their understanding of Mrs. Wright's situation. The other options pertain more to character traits or internal feelings rather than an external action that spurs a discovery.