2007年我国农村取消了农业税，外国人称之为“中国农业的一场革命”，这将大大促进我国农业的发展．这体现了对农业生产产生巨大影响的因素是（　　）

矿泉水中元素及国标含量如表所示，请用化学用语回答下列问题．

①矿泉水中含有的镁元素____；

②久置的水中溶有一定量的氧气，请表示出n个氧分子____；

③表中的一种阴离子____等；

④硫酸钙中钙元素的化合价____．

圆$C_1:{\left(x+2\right)}^2+{\left(y-2\right)}^2=1$与圆$C_2:{\left(x-2\right)}^2+{\left(y-5\right)}^2=16$的位置关系是（   ）

    If someone is lost in a forest( 森林 ), he needs only study the trees around him carefully to find his way. On this half of the earth, he will find that the side of the tree with the most leaves and branches(树枝 ) is the south side. Also, by checking the tops of the trees, he will find that they lean(倾斜 ) to the south too.
    Another sign( 标志物) for him to know where he is going is found in the bark.( 树皮) That is brighter on the south side.The remanining(树桩 ) of a cut tree is also a finder, for its rings can give him another sign. The rings will be thinner on the south side and thicker on the north side.
One more sign: some very small plants grow at the foot of a tree and they point to the north.