题干
— How many children are there in your family?
— There is .
A：only two
B：only one
C：only some
D：some
答案(点此获取答案解析）
B
— How many children are there in your family?
— There is .
A：only two
B：only one
C：only some
D：some
”型木块放在光滑水平地面上，木块的水平表面AB粗糙，与水平面夹角θ＝37°的表面BC光滑。木块右侧与竖直墙壁之间连接着一个力传感器，当力传感器受压时，其示数为正值；当力传感器被拉时，其示数为负值。一个可视为质点的滑块从C点由静止开始下滑，运动过程中，传感器记录到的力和时间的关系如图（b）所示。（已知sin37°＝0.6，cos37°＝0.8，取g＝10m/s2。）求：