亲贤臣，远小人，此先汉所以兴隆也；亲小人，远贤臣，此后汉所以倾颓也。先帝在时，每与臣论此事，未尝不叹息痛恨于桓、灵也。侍中、尚书、长史、参军，此悉贞良死节之臣，愿陛下亲之信之，则汉室之隆，可计日而待也。

问题解决﹣﹣测量电阻：

小雨想要知道未知电阻R_X的阻值，现有一个电压恒定的电源（电压值未知）、一个单刀双掷开关、一个量程较小的电流表、两个阻值分别为R₁和R₂的定值电阻与若干导线，其中R₁和R₂的阻值都较小，均不能单独与电流表串联在电源两端，否则会损坏电流表．

    Eleven countries are building a great wall of trees across Africa. It is called the Great Green Wall. The aim is to bring life to the dry lands and help to fight the bad environment.

    The wall is 8, 000 kilometers long and 15 kilometers wide. It covers from Senegal in the west to Djibouti in the east, on the south of the Sahara Desert (撒哈拉沙漠). So far, Senegal has made the best progress by planting about 11,000,000 trees.

    Many years ago, there were few trees in that area and the winds used to be very strong. It was harmful to the fields. Also, there was little rain, so few plants could grow and many people went hungry. Since the tree planting project started, the trees have provided food for the local people and increased the wetness (湿度) of the air. Little by little, there appeared green fields for people to grow plant.

    The project which began in 2007 is supposed to cost a total of 8, 000, 000, 000 dollars. Many countries are trying their best to help to continue the planting. So we will be able to see the whole green wall across Africa in the near future!