OMTEX CLASSES: What did Rene Descartes insisted upon?

What did Rene Descartes insisted upon?

a. Rane Discartes was the foremost among scholars who insisted on verifying the reliability of historical documents by critically examining them.
b. Among the rules given by him in his book, ‘Discourse on the method’, the following is supposed to have a great impact on the scientific method of research.
c. Never to accept anything for true till all grounds of doubt are excluded.