You didn't tell us the choices that come with the question. So there's no way to help you choose the right one. Here are a few pairs of words that could go in the blank:. Pond:goldfish. ... River:Salmon. ... Atmosphere:Bird. ... Lake:Trout. ... Ground:Nightcrawler. ... Polarcap:Polarbear. ... Dead tree:Termite. ... Live tree:Squirrel.