老师和颜悦色地说：“提起杨桃，大家都很熟悉。但是，看的角度不同，杨桃的样子也就不一样，有时候看起来真像个五角星。因此，当我们看见别人把杨桃画成五角星的时候，不要忙着发笑，要看看人家是从什么角度看的。我们应该相信自己的眼睛，看到是什么样的就画成什么样。”

    Honey(蜂蜜）from African(非洲）forest is very delicious.

    Most people and many animals like eating it. However, the only way for them to get that honey is to find a wild bees' nest(蜂巢）and take honey from it. Often, these nests are high up in trees, and it is difficult to find them. But in parts of Africa, people and animals have a strange helper — a little bird called a honey helper.

    In fact, the honey helper does not like honey, but it likes the wax(蜂蜡）in the nest. The little bird cannot reach the wax because it is inside the bees' nest. So, when it finds a nest, it looks for someone to help. The little bird sings loudly to get the attention(注意） of both passing animals and people. When it has their attention, it flies through the forest, waiting for the following animal or person that loves honey. Then it helps them find the nest. When they finally arrive at the nest, the follower tries to get the delicious honey and the bird waits and watches. Some of the honey and the wax always fall to the ground, and this is when the bird takes its share.

    Scientists do not know why the bird likes eating the wax, but they seem to be able to smell the wax far away.

某炼铁厂用赤铁矿（除含氧化铁外，其余成分不溶于水也不与酸反应）炼铁，欲测定赤铁矿中氧化铁的质量分数，请回答下列问题：

下图是三峡工程建成后宜昌至武汉河段累计冲刷量预测图。据此完成下面各题。