例二（剑五P89 Flawed Beauty: the problem with toughened glass）
Complete the summary with the list of words A-P below.
Toughened glass is favored by architects because it is much stronger than ordinary glass, and the fragments are not as 18________ when it breaks. However, it has one disadvantage: it can shatter 19________. This fault is a result of the manufacturing process. Ordinary glass is first heated, then cooled very 20________. The outer layer 21________ before the inner layer, and the tension between the two layers……These are unstable, and can expand suddenly, particularly if the weather is 22________. If this happens, the pane of glass may break. The frequency with which such problems occur is 23________ by glass experts…….