使用酸度计测试土壤pH值的过程中，必须保持电极（）。
A.清洁
B.卫生
C.不极化
D.极化
参考答案：A
More foreign leaders have sent telegrams and letters recently to _____ China on the complete success of the
Beijing Olympics between Aug. 8 and 24. [ ]
A. congratulate
B. celebrate
C. express
D. expect
Only under special circumstances ______ to take those rests.[ ]
A. are freshmen permitted
B. freshmen are permitted
C. permitted are freshmen
D. are permitted freshmen
