ass日本风韵熟妇pics男人扒开女人屁屁桶到爽|扒开胸露出奶头亲吻视频|邻居少妇的诱惑|人人妻在线播放|日日摸夜夜摸狠狠摸婷婷|制服 丝袜 人妻|激情熟妇中文字幕|看黄色欧美特一级|日本av人妻系列|高潮对白av,丰满岳妇乱熟妇之荡,日本丰满熟妇乱又伦,日韩欧美一区二区三区在线

Plow is a main tool of agricultural farming all over the world. The effects of using a plow are different when it connected with other component or with different designing ideas. The Chinese plows and those made in Europe and America are quite different in structures from the early time. The cover of share of the Chinese plows (lei si) was protruding with triangle shape while the European ones (made of tree trunk) were narrow plate share with a wide sunken moldboard shape. Coming with the iron age, the plows had to be fit with iron share. However the different of share shapes still reserved and inherited in their developing process. The development of both shares in various eras (with many historical figures of both plows) was compared and their principles of soil cracking and effects of ecology and economy were emphasized and evaluated.