Printing traditionally has been defined as a technique for applying under pressure a certain quantity of colouring agent onto a specified surface to form a body of text or an illustration.

印刷传统上被定义为一种通过压力把一定量颜料施加上一特定表面，从而形成文本或图画的技巧。

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The library writes off a certain quantity of books each year.

图书馆每年都注销一定数量的图书。

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Air is a mixture of gases with a certain quantity of solids and usually some liquids mixed in.

空气是各种气体的混合物，其中也含有一定量的固体，也往往混有某些液体。

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And would it be better to buy a part on the spot market or get a supplier to guarantee a certain quantity?

ECONOMIST: Chain reaction

"If they decide that everyone needs to eat broccoli, " then the commerce clause could allow Congress to require everyone to buy a certain quantity of broccoli, the judge said.

WSJ: States Ask Judge to Throw Out Health Law