完形填空（共10小题；每小题２分，满分20分）
阅读下面短文，掌握其大意，然后从21－30各题所给的ABC和D项中，选出最佳选项．
The finest and most sought-after violins were handcrafted by an Italian violin maker over 250 years ago. The man’s name was Antonius Stradivarius. He was born in 1644 and began his career 21 a violin maker’s apprentice (学徒). Working on his own by 1680, he became determined to make 22 that could reproduce tones as rich as those produced by the human voice.
He 23 several shapes and styles for his violins until he arrived at a design that pleased him. During his career he crafted 1,100 violins. Those in 24 have become treasured possessions.
Unfortunately, the secret of the Stradivarius violin died with its maker. During his lifetime Stradivarius kept his notes safely 25 , even his two sons, who helped him in his workshop, did not know all the steps involved in each violin’s construction.
Through the years, many experts have offered 26 explanations for the unique tone of a “Strad”. Some say it is due to the violin’s shape. Others suggests that the secret 27 the special properties(特性) of the wood, which Stradivarius obtained from native Italian trees that no longer exist. The most widely accepted explanation is that it is created by the varnish（清漆） that 
the 28 used to coat his violins. Chemists have analyzed as closely as possible the varnish and have found its 29 has improved the sound of many violins. 30 , no other violin maker has been able to fully reproduce the tone of the Stradivarius’s violins.
21. A. with B. as C. for D. from
22. A. Instruments B. facilities C. equipment D. tools
23. A. investigated B. surveyed C. tested D. experimented
24. A. fashion B. existence C. possession D. use
25. A. protected B. buried C. hidden D. covered
26. A. possible B. accurate C. detailed D. persuasive
27. A. brings in B. takes in C. results in D. lies in
28. A. master B. violinist C. expert D. user
29. A. attention B. application C. invention D. foundation
30. A. Additionally B. Luckily C. Therefore D. Still