Which sentence uses dashes correctly?
a. there on the stage was—my sister!
b. the coat—one of the most colorful that i've seen, seemed to be made of string.
c. today we studied—a poem, did an experiment, and multiplied fractions.
d. i'd love to stay and talk, but—yikes! i'm really late now.

one of the central themes of edward abbey's work has been his staunch opposition to the glen canyon dam on the colorado river that created lake powell, destroying stunning scenery and wildlife habitat, endangering many rare species of fish and animals, and also irreparably destroying many important archaeological sites which provided information about the early inhabitants of the united states.