Have you read the book called Uncle Tom's Cabin? It's said that it is one of the greatest books in America．The book ____an unpleasant social problem—slavery(奴隶制)in the Southern States of America. It first came out in 1852．Over 300,000____were sold out in a year．People had ____ideas about the book．In the North, more and more people began to____theft support(支持)for the freedom(自由)for the black people after they read the book, but in the South, many people were very____at the people in the North. In 1861, the war between the two parts of the country____. Uncle Tom's Cabin surely played a part in the ____. In 1862, Abraham Lincoln met Harriet Beecher Stowe, the book's ____. As he took her hand. Lincoln said, "So this is the little lady who started this big war."

护士给病人输液时，药水瓶上插着两根管，一根给病人输液，另一根通过瓶盖扎进瓶内药水中，如图所示．这根“闲置”管是为了利用 ____．由于针头较细，为确保药液的流速，需要将药水袋提升到相对针管一般不低于1.3m的高度，由此推算针管处受到的液体压强为 ____Pa．（ρ_药液=ρ_水）

欧洲人在评价一项发明时说：“它武装了人类，使虚弱无力的双手变得力大无穷，健全了人类的大脑以处理一切难题。它为机械动力在未来创造奇迹打下了坚实的基础，将有助于报偿后代的劳动。”这项发明是（　）

双曲线$\frac{x^2}{4}-\frac{y^2}{12}=1$的焦点到渐近线的距离为（   ）。