Does your house have a concrete roof or a thatched one? What is your main cereal? Do you have internet access - or just a basic mobile phone? And how many married couples live under your roof? These are among the 33 questions that more than a billion Indians will be asked as the country launches the world's largest census on Wednesday, marking the first population count in more than 15 years. The two-phase exercise, billed as the world's most ambitious of its kind, will see more than three