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.
