Building Materials
When a brick is immersed in water for 24 hours and then dried, if

All listed here
50 percent surface is covered with grey or white deposits, the brick has serious efflorescence
No grey or white deposits appear on the surface, the brick is free from soluble salts
10 percent surface is covered with grey or white deposits, the brick has slight efflorescence

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Building Materials
In the method of condensation polymerization,

The reaction proceeds with an evolution of hydrogen chloride
Low-molecular substances are removed from the high molecular substance
All of these
The reaction proceeds with an evolution of ammonia

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