A tunnel is an educated hole in the ground. It may have two entrances or only one. It may be for moving people or storing freight, water, utility lines, electric power generators, or other things.

Tunnels are mostly used in mining. Mining techniques are special, however, and rarely resemble "true" tunneling. The next most common use for tunnels is to move water (including moving it out of mines). Water supply tunnels were built in the ancient world, sometimes for considerable distances. One tunnel, explored by modern archeologists, was driven 3,000 feet through the base of a hill on the Greek island of Samos in the sixth century B.C. Herodotus, the Greek historian, thought the Samos tunnel was one of the greatest engineering feats of his time. The Greek tunnelers failed to meet in the middle. The two tunneling gangs missed each other under the hill and had to engineer a double hairpin turn to finish the job.

Q. Underline the sentence which supports the conclusion reached in question No. 2.