Chewing gum

(Open cloze)

Instructions
For questions 1-10, read the text below and write the word which best fits in each space. Use only one word in each space.


Up until WWII, chewing gum (1)……….. made of a substance called chicle mixed with flavorings. Chicle is a latex sap that comes from the sapodilla tree (native (2) ………. Central America). In other words, chicle is a form of rubber. Just like rubber bands don't dissolve when you chew them, (3) ……………. does chicle. Chicle is a good bit softer (4) ………….. rubber bands and happens to soften more (5) ……….. it gets warm in your mouth. If you freeze chicle with ice, it gets very stiff -- chicle hardens and softens over a pretty narrow temperature range.
After WWII, chemists learned (6) ………….. to make artificial gum bases to replace chicle. These gum bases are essentially synthetic rubbers (7)…………. have the same temperature profile (8)…………….. chicle.
Gum bases, (9) ………….. natural or artificial, are mixed with sugar and other flavorings to make chewing gum. When you chew it, the rubber releases these flavorings (10) ……………. your mouth. ­

 You will find the key in the first comment.