i was listenning to () wonderful piece of music when there was() _英语解答

i was listenning to () wonderful piece of music when there was() knock on the door
A a ;an B /;a C a;a D the;the

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解答

C 特指的时候用the 后接元音的时候用an 其他时候用a
这里有个固定词组：a piece of