物块M位于斜面上，受到平行于斜面的水平力F的作用处于静止状态，如图，如果将外力F撤去，则物块：（    ）

A．会沿斜面下滑

B．摩擦力方向一定变化

C．摩擦力的大小变大

D．摩擦力的大小变小

a. How could I excite my students and show my warmth, so that they could enjoy their study in English I had a deep thought. b. In order to save my face,I just criticized them seriously whenever they talked in class or even moved a little c. It was smile. There was a kindness called smile. It was the most beautiful language in the world. It could make distance disappear. d. Then I realized my frozen eyes made the students seared and my aerious face took any excitement away from the children’s hearts. e. The next day,I stood on the stage with a smiling face, asking questions with a smile and encouraging the children in a friendly way. I could find happiness and excitement in their eyes ! f. I could control the class now, but the atmosphere became strange. No, they were not listening to me. g. It was too quiet. The breathless silence urged me to consider the way I was teaching. h. I remember,five years ago, when I stood at the teacher’s desk for the first time, the students in my class paid no attention to me,didn’t behave themelves at all. I felt helpless. i. Gradually,they got used to my smile and encouragement. The class became a lovely one. I was moved,and said , "Thank you for listening,boys and girls!" j. "Just awake the students with a smiling face"I said to myself.

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