设A为4×3阶矩阵，且r（A）=2，而B=$\begin{array}{ccc}1& 0& 2\\ 0& 2& 0\\ -1& 0& 3\end{array}$，则r（AB）=____ ．

任务型阅读

    My name is George．I'm from England．Now I'm studying in Germany．I get to school at 7：30 every morning．I find many of my schoolmates come to school by bike．  ①   

    This is an interesting thing for me．In England people usually drive，take a bus or walk somewhere，for example，to school．In Germany, I often see people，even people over eighty years old going somewhere by bike．It makes me think：  ②   

My father gives the answer．We are living in Northern Germany．It is very flat(平坦的).So it is easy for people here to go somewhere quickly by bike .And it's cheaper than(比…….便宜)going by car or by bus．Also,it's good for the environment(环境)．

    I like riding bikes now．   ③    When I go back to England，I will ride more and ask my friends to ride with me．I think they will like tiding bikes，too．

根据材料内容完成下列任务。

课内阅读《父亲的菜园》。

    以后的日子，我们便四处拾粪。有时候我在山坡上放牛，尿憋急了，父亲也要我跑到菜地里去撒。在父亲的精心伺候下，原本贫瘠的死黄土，变得黑亮，锄头挖下去，还能翻出蚯蚓来呢。远远望去，父亲的菜园就像一块碧绿的翡翠，嵌在荒凉的山坡上。

    直到现在，那一块坡地，仍是我家的菜园。春有菠菜、莴笋，夏有黄瓜、茄子，秋有辣椒、南瓜，冬有萝卜、白菜。一年四季，都是一片诱人的翠绿。

①从文中的词语__________可以看出父亲很热爱这块土地。

②为了给土地育肥，父亲和我是怎么做的？

如图是研究“物体动能大小与哪些因素有关”的实验装置，实验中木块被推动的越____ ，表明钢球动能越大，这个实验是为了验证钢球动能大小与____ 的关系。