1. —Where is the bird? 
   —It ________ (fly) away a moment ago.
2. He is worried about _________ (not pass) the English exam.
3. Amy would rather ___________ (wear) green than red. Red is a girl's color.
4. He told me that he would have some difficulty                 (chat) with American students.
5. It is generous of the people from the rich family_________ (donate) to UNICEF.
6. — Hi, Liu Tao. I didn't see you at the party.
    —Oh. I _______ (get) ready for the maths exam.