V. Fill the gaps with the suitable derivatives of the word given on the right

One of the man’s … building materials is finding its way into a lot of new places these days. Concrete first discovered by the Romans, is now more … used in construction than all other materials together. Concrete is a synthetic stone which can be formed while soft into … any shape the builder wants. Portland cement … with water is the paste that binds sand, gravel, clinker into an … rock that becomes … as the years pass. It was called Portland because Joseph Aspolin, the English … who invented the first … scientifically made cement thought it resembled the rock excavated on the isle of Portland on the Dorset Coast.

VI. Read the passage and answer the question: Why does prestressing significantly reduce the amount of structural materials?

Often concrete is the main construction material in modern bridges. Reinforced concrete to which emplanted steel bars add strength, was introduced in 19^th century; its first significant application was in an arched bridge built in France in 1898. Engineers later learned to apply tension to the bars before pouring the concrete. This process called prestressing significantly reduces the amount of structural materials needed for a bridge. Prestressed concrete bridges often have a graceful look which cannot be achieved by iron and steel bridges with their geometric configurations.