20.Only then _____ I _______ ______ my mistake.

　 Only then _____ I _______ _______ I was wrong.

19.It was several minutes before I _____ ________ _____(意识到) what was happening.

18.I can’t accept your kind invitation because of a p__________ engagement.

17.This railway c_______ Beijing with Taiyuan.

16.Creative thinkers try to make c___________ that may seem strange at first.

15.I lost your address, o________ I ______ _______ visited you long before.

14.He’s naughty but o_________ a good student.

13.There is no p________ that a boy of ten can swim across the river.

12.One of the provinces _______ ______ _____ the union and formed a new country.

11.My mother is p_______ to my little brother.