When do we use difficulty (singular) vs. difficulties (plural)? I'm going to explain this and also teach you a number of collocations, typical combinations of words, to expand your vocabulary! Learning collocations improves your English fluency because instead of trying to put a sentence together word by word, trying to think "which verb goes with this noun?" or "which adjective sounds more natural?" – instead, you'll already know combinations of words that go together. My e-book, 1000 collocations in 10 minutes a day, makes learning collocations quick and easy. It has 50 short lessons, 50 quizzes, and comes with audio as well.