People often think the grass is always greener on _________ side of the fence (篱笆).     

在测定小灯泡的额定功率（额定电压为2.5V）的实验中：

化学无处不在．

（1）吸烟有害健康．燃着的香烟产生的烟气中含有一种能与血液中血红蛋白结合的有毒气体，它是____ ．

（2）常温下测得某苹果汁的pH值为3，说明该苹果汁呈____性．

（3）胃酸的主要成分是盐酸，服用含氢氧化铝的药物可以治疗胃酸过多症，用化学方程式说明原因____ ．

（4）化石燃料日趋枯竭，人们正在利用和开发许多其他能源，如太阳能、氢气、地热能、潮汐能，其中可作为未来汽车能源的是____ ．

    The Silk Road is a historically important international trade (贸易) route between China and the Mediterranean (地中海). It began during the Western Han Dynasty and has been a bridge between East and West for over 2, 000 years

    The ancient road started from Chang'an (now Xi'an) and ended in Eastern Europe, near today's Turkey and the Mediterranean Sea. It was about 6, 500 kilometers long and went across one­fourth of the planet.

    The Silk Road got its name in the 19th century because Chinese silk used to be carried along this road. Silk, jade, ceramics and iron went west to Rome. And from the west came glass, gems and food like carrots.

    The Silk Road was very important to both China and the rest of the world. It was more than an ancient international trade route. Besides trade, knowledge about arts, science and literature, as well crafts and technologies was shared across the Silk Road. In this way, languages and cultures developed and influenced(影响)each other.

    Today, China is trying to build the“21st Century Marine(海洋的)Silk Road”. With the help of APEC held in Beijing in November 2014, the dream of One Belt One Road(the “Silk Road Economic(经济的)Belt” and “21st Century Marine Silk Road”(“一带一路”)is coming true.