参考：1、《than引导比较状语从句时，究竟是从属连词还是关系代词/关系副词》

           2、《关于曹老师的《than引导比较状语从句时，究竟是从属连词还是关系代词/关系副词》自己的两个疑问》 

原文：The Crystal Palace

  Perhaps the most extraordinary building of the nineteenth century was the Crystal Palace, which was built in Hyde Park for the Great Exhibition of 1851. The Crystal Palace was different from all other buildings in the world, for it was made of iron and glass. It was one of the biggest buildings of all time and a lot of people from many countries came to see it. A great many goods were sent to the exhibition from various parts of the world. There was also a great deal of machinery on display. The most wonderful piece of machinery on show was Nasmyth's steam hammer. Though in those days, travelling was not as easy as it is today, steam boats carried thousands of visitors across the Channel from Europe. On arriving in England, they were taken to the Crystal Palace by train. There were six million visitors in all, and the profits from the exhibition were used to build museums and colleges. Late, the Crystal Palace was moved to South London. It remained one of the most famous buildings in the world until it was burnt down in 1936.

我的理解1：‘travelling was not as easy as it is today’，这里第二个as是连词，方便理解我认为是比较代词替代traveling。复原为‘travelling was not as easy as it is traveling today.’网上说traveling was not as easy as today.我认为错的，因为比较项主语和谓语不一样，所以不能省略it is..

我的理解2：      He often eats more than is good for his health.复原为      He often eats more than （it） is good for his health that he should eat.