Prolific science writer Susan E. Goodman has delighted young audiences with her informative- and always entertaining- works. In It's a Dog's Life, Goodman explores such canine quandaries as, ''Why do dogs sniff everything?'' and ''What do they see when they look at a sunset?'' Goodman's engaging, humorous writing style grabs young listeners and proves the perfect vehicle for offering choice tidbits on canine evolution, breeds, and behavior.