柴油机纸质滤芯精滤器是由主滤芯和（）两层构成。
A.干式滤芯
B.湿式滤芯
C.旋风式滤芯
D.安全滤芯
参考答案：D
The murderer was brought in, with his hands _____ behind his back.
A．being tied
B．having tied
C．to be tied
D．tied
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