唐代和宋代都有谏官。唐代谏官由宰相荐举，主要评议皇帝得失；宋代谏官由皇帝选拔，主要评议宰相是非。这说明

   The aim of students who came to school is to study. But to study requires (需要) a right way, or you waste either the time or the money. The following are the ways of studying.
   The best time for reading is morning, because in the morning, the air is fresh and the mind is clear. For that reason, we can get good result.
   In studying we must have patience (耐心). If we have not known a text well, we must read it again. We should not read the next one till we have learned the first one.
   When we are studying, we must put our hearts into the book, or we can get nothing from the book while we are reading.
   We must always ask “whys”. If it is not well understood, write it down and ask our teachers or our parents, or friends. In any possible way, we must know it completely and what we've learned can be used well and made better.
   Though there are many ways for studying, yet the above mentioned will be quite enough if we can keep them in heart and do so.

已知三点P₁（x₁，y₁），P₂（x₂，y₂），P₃（1，-2）都在反比例函数y＝^{$\frac{k}{x}$}的图象上，若x₁＜0，x₂＞0，则下列式子正确的是（　　）

阅读下面这首词，回答问题。

宿桐庐江寄广陵旧游

孟浩然

山瞑听猿愁，沧江急夜流。风呜两岸叶，月照一孤舟。

建德非吾土，维扬①忆旧游。还将两行泪，遥寄海西头。

【注释】①维扬：扬州的古称。

孑孓是蚊子的幼虫，适于生活在水中。某同学提出“生活在水中的孑孓需要空气吗?”请你设计一个实验帮他探究该问题

甲                         乙
（一段时间后孑孓衰弱或死亡）    （一段时间后孑孓正常生活）
　探究提示
　提出问题：生活在水中的孑孓需要空气吗?
（1）作出假设：____ 。
（2）实验设计：
　A.本实验的变量时什么？____ 。除实验变量不同之外，其他条件是否应该相同？____ 。
　B.本实验如图所示，____ 图是实验组，____  是对照组。
（3）预期的实验结果：____ 装置中的孑孓一段时间后衰弱或死亡；____ 装置中的孑孓一段时间后仍然正常生活。
　试分析出现该结果的原因：____ 。
（4）得出结论：____ 。