From the context of the given sentences we can understand that the given sentence is a comparative advice. It advises someone to learn to invoke and to recognize as his/her ancestors did. The structure given in B and D is 'He must learn as they learnt' which is incorrect as the correct structure should be 'Hemust learn to recognize as they did' In A we are given that 'as did the ancient in India centuries ago'. This is unclear as we not sure what 'it' here is referring to. It may either mean invoke or recognize. Thus, only option B is correct