Read the passage and choose the correct answers.

The Galapagos Islands are the home to some of the last giant tortoises left on earth. Hundreds of years ago, thousands of tortoises wandered around these islands. However, all that changed when people started landing there. Sailors used to row ashore and seize as many tortoises as they could. When the ani¬mals were aboard the ship, the sailors would roll the tortoises onto their backs. The tortoises were completely helpless once on their backs, so they could only lie there until used for soups and stews.

The tortoises faced other problems, too. Settlers arrived bringing pigs, goats, donkeys, dogs and cats. Donkey and goats ate all the plants that the tortoises usually fed on. Dogs and cats consumed thousands of tortoise eggs each year. Within a few years, it was hard to find any tortoise eggs - or even any baby tortoises.

By the early 1900s, people began to worry that the last of the tortoises would soon die out. No one, however, cared to do anything about the problem. For another fifty years, this situation continued. Finally, in the 1950s, scientist decided that something must be done. The first part of their plan was to get rid of as many cats, dogs and other animals as they could. Next, they started looking for wild tortoise eggs. When the eggs hatched, the scientists raised the tortoises in special pens. Once the tortoises were old enough and big enough to take care of themselves, the scientists took them back to their islands and set them loose. This slow, hard work continues today, and thanks to it, the number of tortoises is now increasing every year.

The mountain climbers _________ the ravine without a guide.