下列实验操作正确的是（  ）

如图所示，轻质杠杆AD用两根软绳悬挂于天花板上，两绳分别系在杠杆上的B、C两点。已知杠杆的长度为0.8m，BC间的距离为0.2m，CD间的距离为0.2m。用细绳将滑轮组固定在杠杆的A端，物体E（其质量可变）挂在动滑轮的挂钩上，每个滑轮重均为60N。物体H通过细绳挂在杠杆的D端，其质量始终保持不变。为使杠杆AD保持水平平衡，滑轮组所能提升重物E的最大质量m₁与最小质量m₂之比为4:1。杠杆、细绳的质量及一切摩擦均可忽略不计，取g= 10N/kg。求：

（1）滑轮组对杠杆A端的最大拉力F_A1与最小拉力F_A2之比；
（2）重物E的最大质量m₁；
（3）滑轮组的最小机械效率。（百分号前保留整数）

1989年东欧剧变对我们有哪些启示(      )

①坚持独立自主的内外政策                         ②大力发展生产力，发挥社会主义制度的优越性

③学习苏联的政治体制                                ④加强执政党的建设

短文填空 (注意适当形式)

     To many people, American food means____ , hot dogs and fried chicken. If you like sweet (甜的)____ , you may even think of apple pies (苹果派) or chocolate cookies (曲奇饼干). It's true that Americans often____ hese things.

     It's hard to find another traditional American food except (除.....之外) Thanksgiving ____ . The United States is a land of people who come from____ countries.  When the people come to America, they____ their cooking styles with them, too. So in America you can find other countries'____ . For example, they____ Italian pizzas, Mexican tacos and Chinese egg rolls. However, these foods in American aren't quite____ the original (原先的) ones in other countries.