根据句意和所给首字母补全单词。（共15题，每小题1分，满分15分）

1.Milk, water and oil are all l_____ while wood, iron and glass are solids.

2.You can easily find the site by entering the k_______ “Quark”.

3.Water is recognized as the s_____ of all life. Without it, there would be no life.

4.She was born in a         (富裕的) family.

5.The old man had no a________ to education when he was young.

6.Helen is____________ (担心的) about traveling on her own.

7.I think it’s only an o_________ camera and I needn’t pay such a high price for it.

8.Living in the business d_______ of a city provides a great convenience for shopping.

9.As students, we must c____________ our attention on our lessons.

10.People are concerned about the quality of the air they___________ (呼吸).

11.Children should be encouraged to be __________（独立的）thinkers. 

12.Helen is the most diligent shop____________ (助手) that I have ever seen.

13.She lost the d_______ necklace that she borrowed from one of her friends.

14.She has read many of the major works of _________ (文学).

15.The _________ (百分率) of overweight people around the world has been increasing these years.