Option a is the correct answer The most important feature of Indus valley civilization is the use of burnt bricks. Harappans used baked and unbaked bricks, and stones for construction. The towns had a grid pattern and drainages were systematically built. The houses were built of mud bricks while the drainages were built with burnt bricks. The Indus Valley people were the first to use burnt bricks on a large scale. They built some of the most impressive brick structures in the ancient world, such as the Great Bath at Mohenjo-daro and the Citadel at Harappa