题目

Is early childhood education necessary? Early childhood education    13    learning through playing to help with children’s physical, communicational and social development. Early childhood education has become a     14    of the government today. There are many reasons for the government to    15    early childhood education. Studies have shown that children who did not    16    good care or education will become developmentally (身心发展地) delayed, causing    17    in school, and even in life easily． Experts also find there are    18   �如图所示，用细绳系着一个小球，使小球在水平面内做匀速圆周运动，不计空气阻力，以下关于小球受力的说法中正确的是（ ）A．只受重力B．只受拉力C．受重力、拉力和向心力D．受重力和拉力