It ______ long ago that the earth is round. A: was discovered B: is discovered C: discovers D: discovered

They discovered the cause of the fire accidentally. They discovered it _________.

While building a tunnel through the mountain, ________. A: an underground lake was discovered B: there was an underground lake discovered C: a lake was discovered underground D: the workers discovered an underground lake

Madame Curie is believed ____ the radium. A: discovering B: having<br/>discovered C: to have discovered D: to discovered

DNA is very useful for us, it many years ago. (1.0) A: discovers B: discovered C: is discovered D: was discovered

Last summer, We visited the cave ___which Peking man was discovered.

Pluto, the outermost planet of the solar system, _____photographically in March 1930. A: discovered B: was discovered C: by discovery D: when discovered

He became very friendly when he ____________ that she was my sister. A: was discovered B: discovers C: has discovered D: discovered

The flight was postponed because of technical problems and was finally cancelled last week when a ______ was discovered.

She was quite right,___ Harry soon discovered. A: which B: that C: as D: what