Compound words are formed when two or more words are put together to form a new word with a new meaning. Since a, <em>whitewash </em>can be separated to <em>white wash, </em>it is a compound word. Since b, <em>watchdog </em>can be separated to <em>watch dog, </em>it is a compound word. Since d, <em>buttercup </em>can be separated to <em>butter cup, </em>it is a compound word. But C, if it was split up, cannot be any real word. C is the only non compound word in the answer choices.
