问题
单项选择题
在跳汰选煤过程中，对于相同原料煤，可采取增大用水量的方法来增大（）值，从而增大干扰沉降速度。
A、容积浓度
B、松散系数
C、浓度系数
D、松散浓度
答案
参考答案：B
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在跳汰选煤过程中，对于相同原料煤，可采取增大用水量的方法来增大（）值，从而增大干扰沉降速度。
A、容积浓度
B、松散系数
C、浓度系数
D、松散浓度
参考答案：B
Even though it was only October, my students were already whispering about Christmas plans. With each passing day everyone became more 31 waiting for the final school bell. Upon its 32 everyone would run for their coats and go home, everyone except David David was a small boy in ragged clothes. I had often 33 what kind of home life David had, and what kind of mother could send her son to school dressed so 34 for the cold winter months, without a coat, boots, or gloves. But something made David 35 . I can still remember he was always 36 a smile and willing to help. He always 37 after school to straighten chairs and mop the floor. We never talked much. He 38 just smile and ask what else he could do ,then thank me for letting him stay and slowly 39 home. Weeks passed and the 40 over the coming Christmas grew into restlessness until the last day of 41 before the holiday break. I smiled in 42 as the last of them hurried out the door. Turning around I saw David 43 standing by my desk. “I have something for you” he said and 44 from behind his back a small box. 45 it to me, he said anxiously, “Open it. ”I took the box from him, thanked him and slowly unwrapped it. I lifted the lid and to my 46 saw nothing. I looked at David’s smiling face and back into the box and said. “The box is nice, David, but it’ s 47 . ” “ Oh no it isn’t ,” said David “ It’s full of love, my mum told me before she died that love was something you couldn’t see or touch unless you know it’s there .” Tears filled my eyes 48 Ilooked at the proud dirty face that I had rarely given 49 to. After that Christmas, David and I became good friends and I never forgot the meaning 50 the little empty box set on my desk.
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