Burning all the lights in the classroom will be a great______ on electric power.

China sent up two manned spaceships and they were also great scientific _______ in the world.

Soon after the mud-rock flow hit Zhouqu, Gansu Province, many soldiers came to the ______ as many people were trapped underground.

My father always shouts at me because he is a man with little _________.

In our class, when the bell rang and the teacher closed his book, it was a      for everyone to stand up.