1．A serious lack of water is a real________(屏障，障碍) for people wanting to settle in the desert.
答案： barrier
2．My toothache is________(难以忍受的)，so I must go to see my dentist.
答案： unbearable
3．Although it was a________(复杂的) problem，he solved it in a very simple way.
答案： complex
