明清（鸦片战争前）时期，中国在传统农耕文明的轨道上发展到一个新的阶段。下列对这一时期历史阶段特征最恰当的概括是(    )

下列动物中，运动方式和其他三种不同的是（    ）

如图所示，用3N水平力F拉长木板A在光滑水平地面上运动，而B静止不动时，若逐渐增大F（不计绳和弹簧测力计重），则B受到摩擦力____ （填“变大”、“不变”、“变小”），方向向____ ．

根据短文内容及首字母提示，补全空格内单词，使短文完整、通顺。(请在答题卡上写出完整单词)

    It was sunny and h____ again at this time of year. John went to the beach to s____ his weekend. He was lying on the sand and l____ to music. Suddenly he h____ someone crying for help. He j____ up hurriedly and looked towards the voice. He saw a little boy waving(挥动) his hands in the w____ a little far away. He t____ off his clothes and jumped into the water

    q____ . He swam to the little boy, held him, kept his head a____  the water and swam back to the beach. At last, the boy was safe. He thanked John a l____ .