(21) ...................A. through B. over C. along D. across

Read the following passage carefully, and then select the best option A, B, C or D to complete it

Music, artful arrangement of sounds (21) _______ time. This definition is obviously very broad, but a narrower one would exclude (22) _______ much. Music is part of virtually every culture on (23) _______, but it varies widely among cultures in style and structure. Definitions of music can (24) _______ dramatically over a short time, as they have across the world during the 20^th (25) _________.

Can music exist without (26) _______? Some philosophers argue that music should be defined as a kind of “mental (27) _______” and that the physical aspects of sound are simply by-products of this image. If you (28) _______ you can have a musical experience by imagining the sound of a piece of music, then you think (29) _______ can exist without sound. But most musical experiences involve producing or (30) _______ to physical characteristics of sound such as pitch and timbre (quality comparable to texture or color in sight).

Is the tape-recorded sound of a large metal-stamping machine music? Are 4 minutes (31) _______ 33 seconds of silence music? Is the activity of reading a (32) _______ of hundreds of seemingly unrelated objects, activities, and states of mind music? Each of these “(33) _______”, as well as many other sounds (or nonsounds), has been copyrighted (34) _______ a musical composition, performed, and recorded in the 20^th century. One of the legacies of 20th-century music is to have blurred the definition of music as (35) _______ before.

(21) ...................

• A. through
• B. over
• C. along
• D. across