Slow and progressive deformation of a material with time under constant stress is called________?

Pick out the correct statement?

Which of the following bricks should not be used, if the furnace is to be used intermittently?

Flue gas discharge velocity through chimney of a big thermal power plant may be around ________ m/sec?

Solid particles separation based on the difference in their flow velocities through fluids is termed as the________?

Commercial production of petrol from coal (as practised in a factory at Sasol in South Africa) is done by the ________ of coal?