The correct answer is: C. Is economical for large spans and is adopted now a days.
Post-tensioning is a method of reinforcing concrete structures. It involves the use of high-strength steel cables that are tensioned after the concrete has been poured and cured. This creates a compression force in the concrete, which helps to resist tensile stresses.
Post-tensioning can be used to create structures with long spans, such as bridges and buildings. It can also be used to strengthen existing structures.
Post-tensioning is a relatively expensive method of reinforcing concrete. However, it can be cost-effective for structures with long spans or that require a high degree of strength.
Option A is incorrect because post-tensioning was not widely used in earlier days. It was first developed in the early 20th century, but it did not become widely used until the mid-20th century.
Option B is incorrect because post-tensioning is economical for large spans. It is often used for bridges and buildings with long spans.
Option D is incorrect because post-tensioning is a real and widely used method of reinforcing concrete structures.