🤠ADVANCED English Vocabulary (with sample sentences) - GRE prep

State a noun that describes using every  situation to try to gain power or get an advantage.

Opportunism. Politics is full of greed and opportunism rather than people who actually want to improve society.

What's a word that means a person subject to sudden unpredictable changes of mood or mind, fickle?  

Mercurial. I had a roommate once that was so mercurial she was really difficult to live with.

Give a term for irritable, testy, touchy.  

Irascible. Unfortunately, my grandfather is  becoming more and more irascible as he ages.