71. People in prehistoric times created paints by grinding materials such as plants and clay into power and then adding water.


  72. Often very annoying weeds, goldenrods crowd out less hardy plants and act as hosts to many insect pests.


  73. Starting around 7000 B.C., and for the next four thousand years, much of the Northern Hemisphere experienced temperatures warmer than at present.


  74. When Henry Ford first sought financial backing for making cars, the very notion of farmers and clerks owning automobiles was considered ridiculous.


  75. Though once quite large, the population of the bald eagle across North America has drastically declined in the past forty years.


巧背英语四级100个句子单词[13]: http://insuns.com/article/17793-1.html