_____. Lions and tigers have sharp claws, swiftness and strength; monkeys can climb into trees away from their enemies. Birds can fly, turtles withdraw into their shells. But one of the most fascinating means of protection is deception, the ability many creatures have to camouflage themselves so that they will be missed by their enemies.

Two of the major religions of the world are Christianity and Islam, _____. Both worship the same deity, whom the Christians call God and the Muslims call Allah. For knowledge of his faith and for inspiration, the Christian turns to his holy book, the Bible. The Muslim, too, has a holy book, the Koran, which guides his prayers and gives meaning to his life.

We began our long trek in freezing wind and snow. Before we finished, I knew we would encounter not only harsh winter conditions, but burning deserts and scorching sun. _______. For now, the cold was our worst enemy. Huddled around our tiny fire in our tent at night, we felt we would give anything for the warm sun.

The floppy disk has revolutionised publishing. Before its invention, typed or hand-written documents had to be edited and then completely retyped, whereas now  corrections can simply be typed into a computer. _______ and authors sometimes even lost their only copy while taking it to the publisher. Now entire manuscripts can be copied from one disk to another in an instant.

Any comparison between life at the end of the last century, and of this one would highlight the enormous advances in medicine which many people nowadays take almost for granted. By 1900, clean water and good sanitation had reduced the death rate from infectious diseases. There were no antibiotics, no vaccines, no insulin, and no medicines to treat high blood pressure, ulcers, cancer, or mental illness. Surgery was severely limited by the threat of infection. ______.

_______ It may be simply a few palm trees around a spring, or a larger area where cultivation of crops is possible. The existence of oases makes it possible for nomads to cross the desert in search of pasture for their animals.

The calcium stored in the bones and teeth is constantly being exchanged with the calcium in the blood. _______. However, too much calcium can  be a problem as well, and can lead to the calcification of joints and produce kidney stones in 1952, one of  these stones, weighing nearly seven kilos, was removed from an 80-year-old woman.