21. ________ he was the last man I wanted to see£¬I did all in my power to help him.

A.As        B. Now that         C. While        D. However

22. The doctor began feeling inactive and powerless a couple of days ago, but not until he developed 103-degree fever, ________ Doctors Without Borders, authorities said.

A. did he contact   B. he had contacted   C. had he contacted    D. he contacted

23. The organic food products are made of natural ingredients, with no_____ flavors added.

A .accurate          B. regular         C. superficial      D. artificial

24. In the program aiming to help kids with heart disease, _______ is given to those who are the only child in their family. 

A. preference       B. prejudice       C. recognition       D. compromise

25.Do not make complaints about being left out ________ you shy away from sharing your joys and sorrows with others.

    A. while            B. when           C. unless      D. once