The discovery of how bronze is made was probably accidental, but itto be an important event.

Mr. Wu found that a number of UFOs in the sky ______ in a very short time in surprise.

It’ll be another 50 years _________ China is expected to reach the level of a medium developed country.

How far is the factory from here—It’s about 4 kilometres _______.

Never before ___________in greater need of technical experts than it is today.