39. ask for 要求

    40. attach importance to 重视

    41. pay attention to重视catch one's attention引起…注意/重视

    42. available可得/买到的

    There is no ticket available.

    43.average平均on（the） ~

    44. be aware of = realize意识到be sure一定要，肯定

    He apologized to us for the mistake as soon as he was aware of it.

    Be sure not to be late for the meeting.

    I'm sure the play will be a great success.

    45. back up支持

    46. background背景

    47. base ~…on…把…建立在…基础之上

    His article is based on the research.

    48. bear忍受，容忍同义词：

    endure tolerate stand put up with

    She cannot bear to see the child in pains.

    49. do/try one's best

    He said he would try his best to carry out the plan.

    50. because连词：There will be no meeting because the manager will be on the vacation next week.

    because of介词：His wedding will be put off because of his father's death.