______ birds use their feathers for flight, some of their feathers

25. ______ birds use their feathers for flight, some of their feathers are for other purposes.(C)

A. once B. If C. Although D. Because

26. Jane moved aimlessly down the tree-lined street, not knowing ______she was heading.(B)

A. why B. where C. how D. when

27. Many airlines now allow passengers to print their boarding passes online ______ their valuable time. (C)

A. save B. saving

C. to save D. saved

28. If you don’t understand something, you may research, study, and talk to other people _______ you figure it out.(C)

A. because B. though C. until D. since

29. In the 1950s in the USA, most families had just one phone at home, and wireless phones _______ yet. (D)

A. haven’t invented B. haven’t been invented

C. hadn’t invented D. hadn’t been invented

以上为北京高考英语试卷的部分试题及答案，仅供参考。