用所给单词的适当形式完成句子。
A) extreme
1. I am ______ sorry to have troubled you so much.
2. I am grateful to her for always showing ______ gentleness and kindness to me.
B) suffer
3. He felt pity for a man who had ______ so much.
4. It is hardly possible to forget the ______ caused by the war.
C) express
5. Young children often have difficulty in ______ themselves.
6. Learning more words and ______ plays an important part in language studies.
D) frighten
7. She will be ______ to death when she sees the way you drive.
8. It is ______ to think how easily children can be hurt.
9. Hearing the terrible noise, the girl had a ______ look on her face.
E) congratulate
10. As soon as he met me the next day, he ______ me warmly on passing the driving test.
11. I would like to express my ______ to all of you for such a wonderful performance in the exam.
12. "______ to all of you on your great success!"our coach said the moment he saw us.
F) sincere
13. Finally, I'd like to express my ______ gratitude for your help in this matter.
14. At the end of the letter, we often use the expression "Yours ______".
腈（CH3CN）溶液中加入等体积的水，所得溶液中乙腈的质量分数为0．4a，若乙腈的密度为
，水的密度为
，则下列说法正确的是
