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）
小题1:Milk, water and oil are all l_____ while wood, iron and glass are solids.
小题2:You can easily find the site by entering the k_______ “Quark”.
小题3:Water is recognized as the s_____ of all life. Without it, there would be no life.
小题4:She was born in a         (富裕的) family.
小题5:The old man had no a________ to education when he was young.
小题6:Helen is____________ (担心的) about traveling on her own.
小题7:I think it’s only an o_________ camera and I needn’t pay such a high price for it.
小题8:Living in the business d_______ of a city provides a great convenience for shopping.
小题9:As students, we must c____________ our attention on our lessons.
小题10:People are concerned about the quality of the air they___________ (呼吸).
小题11:Children should be encouraged to be __________（独立的）thinkers. 
小题12:Helen is the most diligent shop____________ (助手) that I have ever seen.
小题13:She lost the d_______ necklace that she borrowed from one of her friends.
小题14:She has read many of the major works of _________ (文学).
小题15:The _________ (百分率) of overweight people around the world has been increasing these years.