题目

笑笑家的煤气表去年12月底的读数是220立方米。下面是笑笑家煤气表今年上半年每月月底的读数。（单位：立方米） 1月底2月底3月底4月底5月底6月底 318405512608726845 （1） 分别算出笑笑家上半年各月份的煤气用业。 （2） 笑笑家今年上半年一共用煤气多少立方米？ （3） 请你再提出一个数学问题并解答。Agricultural experts met in Ethiopia last week to discuss ways to help sub-Saharan Africa become a major producer of wheat．The area traditionally produced little wheat，while North Africa was the grain basket． Wheat production fell sharply in sub-Saharan countries during the 1980s．In the 1960s，attempts were made to grow wheat in sub-Saharan Africa．including South Africa and Zimbabwe．But those countries found it was less costly to import wheat from Europe and the United States．Another problem is that Africa's wheat farms were often far from population centers．There also were transportation issues．And some lowlands were not a good place to grow wheat． Hans Joachim Braun．one of the experts，says now is a good time to increase wheat production．In the last four years we have seen three major price hikes，where the wheat price and other staple process(主食加工)exploded．And that puts a big，big bill on countries which are depending on wheat imports，and Africa is the biggest wheat importer． He also says demand for wheat in sub-Saharan Africa is growing faster than for any other crop．With higher income people would like to have more diversified food．But that is possible not the most important one．The most important one is that there is a tremendous migration of in particular male labor to the cities．And wheat products are convenient food because you can easily buy it．It's easy to process and you also can store it for a few days，which is different from some of the maize and rice products． There are three possible challenges for growing more wheat in Africa：climate change，disease and pests，like insects．Mr．Braun says rising temperatures should not have a major effect on wheat．In fact，he says，it could help wheat grow in areas with high rainfall totals．As for fighting disease and pests，experts suggest growing more resistant crops．In addition，railroads and roads would have to be improved so large amounts of wheat could be moved to large markets． 71．The sharp fall of wheat production during the 1980s is caused by the following except that　　　 ． A．to import wheat from Europe and the United States is economic B．Africa's wheat farms were often far from population centers C．some lowlands were not suitable to grow wheat D．farmers there didn't attempt to grow wheat 72．What does the word“hikes”in Paragraph 3 probably refer to? A．big changes 　　　 B．large increases　 C．long trips 　　　　　　 D．big bills 73．Wheat price exploding indicates　　　 ． A．sub-Saharan countries need to increase wheat production badly B．sub-Saharan countries have to issue more money C．sub-Saharan countries should grow more Corn D．importing much wheat is urgent 74．Higher demand for wheat in sub-Saharan Africa mainly results from　　　 ． A．the large number of hungry people there B．the diversified need of higher income people C．male labor crowding into the cities D．the higher wheat price 75．According to Mr．Braun the main challenges for growing more wheat in Africa are ． A．climate change and disease B．risistant crops and climate change C．rising temperatures and disease and pests D．disease and pests and inconvenient transportation