Many animals move from one place to another at certain times of the years,     1     is called migration. They migrate to find food, seek a partner, or in search of warmer weather.

Every autumn,     2    （million）of the North American monarch butterflies begin a long and difficult journey. They manage to travel around 4,000 kilometers south and get to California or Mexico. However, how they did this was unclear.

A team of scientist has now found that the monarch is able to tell the time of day. It uses its eyes     3    （measure）the position of the sun. It uses the time of day and the point of the sun to determine the way to go and change its     4    （direct）. Eventually, it manages to reach the place     5     it will spend the winter.

In the last few years its population     6    （crash）significantly.     7    （sad），human activity is the main reason why the number of monarch butterflies is falling.

People cut     8     trees and use chemicals, which destroys the natural environment.

The research on the monarch’s behaviour has lead to a greater     9    （aware）of this creature. There may come a time when the number of monarch butterflies increases once again. The     10    （much）we know about this lovely creature, the greater the chance it will survive.

Perhaps the most extraordinary building of the nineteenth century was the Crystal Palace,     1     was built in Hyde Park for the Great Exhibition of 1851. The Crystal Palace was different from all other buildings in the world,     2     it was made of iron and glass. It was one of the     3     buildings of all time and a lot of people from many countries came to see it. A great many     4     were sent to the exhibition from     5     parts of the world. There was also     6     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     7    thousands of visitors across the Channel from Europe.     8     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     9     to build museums and colleges. Later, the Crystal Palace was moved to South London. It     10     one of the most famous buildings in the world until it was burnt down in 1936.