谓语用单数还是复数6.纸和印刷术已经被应用很久了.Paper and printing______ ________ ______for ages.

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谓语用单数还是复数6.纸和印刷术已经被应用很久了.Paper and printing______ ________ ______for ages.
谓语用单数还是复数
6.纸和印刷术已经被应用很久了.
Paper and printing______ ________ ______for ages.

谓语用单数还是复数6.纸和印刷术已经被应用很久了.Paper and printing______ ________ ______for ages.
Paper and printing___have___ __been______ ___used___for ages.
复数,主语有两样东西.

have been used/using