With passage of time the man realised ________

Directions: Given below is a brief passage followed by a question. Read the passage carefully and choose the best alternative out of the four given alternatives.

Before the dawn of civilisation, man overpowered the weak with his physical strength. In the struggle for existence, it was the survival of the fittest. Might be it was right. Man didn't think twice while killing his prey. So, the prehistoric man was almost barbaric and lived solely on the strength of his muscle power. Gradually, man became aware of his intellectual ability. He learned to turn things in his favour by using his brain. He realised he was superior to all in the animal kingdom due to his ability to think. He began using his mind to deal with day-to-day situations.