Put the verbs in brackets into the correct form and read the text. Chewing Gum People (to enjoy) chewing gum-like substances in many lands centuries ago. Some of these materials (to be) thickened resin and latex from certain kinds of trees. Others (to be) various sweet grasses, leaves, grains and waxes. Ancient Greeks, for example, (to chew) mastic gum which they (to obtain) from the bark of the mastic tree. This tree (to grow) on the island of Chios. Grecian women especially (to like) chewing mastic gum to clean their teeth and sweeten their breath. From the Indians, the American colonists (to learn) to chew the gum-like resin that formed on spruce trees when the bark was cut. Lumps of spruce gum (to become) popular and merchants (to sell) them in the eastern United States, making it the first commercial chewing gum in this country. Mexican General Santa Anna (to introduce) such lumps to the inventor Thomas Adams, who (to begin) experimenting with it as a substance for rubber. Adams (to try) to make toys, masks and rain boots, but his experiments (to fail). Sitting in his workshop one day, tired and discouraged, he (to put)...

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