Contacting surfaces of the gate and body seats must be smooth and flat for effective sealing.

闸板和阀座的接触表面必须光滑、平整，才能有效地密封。

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In order to produce high quality single crystal, the solid liquid interface morphology must be smooth, even be plane.

为了获得高质量的单晶，固-液界面面必须平滑，甚至是平界面。

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The working surface must be nonabsorbent and smooth.

画布应该是光滑的和不吸水的。

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The plastic must also be flat and smooth for the reading to be accurate, and the object must be brought to the machine (which is not very portable) for analysis, which takes yet more time.

ECONOMIST: Recycling

The roasting must be even, and the grinding process must be finely calibrated so that the resulting coffee allows smooth passage of the hot water that extracts the flavour.

ECONOMIST: Espresso coffee

As it strives for high-performance characteristics, Lexus must be careful not to alienate the customers who have come to prefer its smooth, comfortable ride, Carter acknowledges.

FORBES: Luxury Wars