At 9.am.that morning,they were having a math class when the head teacher came in and told them the big news.All of them were so excited that everybody was talking about it.A total of 1420 students were watching the live lecture at that time Mingdi was impressed most when the crew were conducting the optics(光学)experiment. Past continuous Form use tense Signal word S+ actions or events that were that was /were happening and were not morning doing finished at the past moment.that morning, they were having a math class when the head teacher came in and told them the big news. All of them were so excited that everybody was talking about it. A total of 1420 students were watching the live lecture . Mingdi was impressed most when the crew were conducting the optics(光学) experiment. were having was talking Form Use Signal word that morning， ... At 9.am. were conducting at that time