選材規(guī)范、標準演練；循序漸進、梯度提升；題量豐富、有效提高；技巧同步、一語中的；縮略速記，全面覆蓋。 The cause of thunder has been a subject of discussion for a long time. In the third century BC, it was believed that 1.__________. However, the most accepted theory was developed in the 20th century. According to this theory, the bolts of lightning are very hot, 2.__________. When this high temperature bolt hits the surrounding air, there is 3.__________, sending out a shock wave, which we hear as a sound of explosion. Thus, thunder is caused 4.__________, near the stroke of lightning 5.____________. In case that you are outside during a thunderstorm, it is advisable to avoid open fields, beaches and lakes and also 6.__________. The safest way is to 7.__________ or stay in the car. <注意>填橫線處的短句，一行一個短句。