Answer : c. gaggle
All the choices above are compound nouns except "gaggle". Compound nouns are words that is made up of two or more words with different meaning that are joined together to create a single noun with an absolutely different meaning from the two previous nouns. Toothpaste is a combination of tooth and paste while bedroom is a combination of bed and room. Lastly, balance beam is a combination of balance and beam. Gaggle on the other hand simply is a noun which refers to the flock of geese.
