Passage 2 　In India, chai is more than just a cup of tea to start the day-the thick sweet drink is an integral part of the rhythm of life. Zach Marks and Resham Gellatly have been documenting the culture of Indian chai and the people who sell it- known as chai wallahs. 　Tea is India's most popular drink-the country consumes 837,000 tons of it every year. The ritual of drinking chai goes beyond all boundaries, and roadsides are dotted with chai wallahs who serve it boiled up with spices（香料），sugar and milk. 　Santosh began selling tea at his shop 15 years ago. The neighboring area in Mumbai has changed dramatically. Many of the small businesses where Santosh once delivered chai have been replaced by large office buildings which he can't enter. But many people working in the new developments have become regular customers, preferring Santosh's chai made with thick milk and fresh ginger to the tea bags available in their offices. 　A popular ingredient in north Indian chai, ginger is believed to have numerous health benefits and is thought to keep your body warm in winter. The spicy root has been used in hot, milk-based beverages in India for hundreds of years, so when the British made tea popular in the late 19th and early 20th centuries, adding ginger to the mix was a natural thing to do. 　Shobhan Barwa's stand is in the heart of Alipore, a fashionable neighborhood in Calcutta. During the annual Hindu festival of Durga Puja, crowds of visitors gather here to see the elaborate pandals-temporary structures housing Hindu gods. He usually closes shop by 22:00, but for the week of Durga Puja, he stays open until 05:00 serving chai, eggs and French toast to visitors who need a caffeine kick to keep them going through the night. 　On the final day of the festival, thousands join a procession（队伍） to the Hooghly River where giant statues of Hindu gods and goddesses are put in the water. Last year, though, celebration turned to tragedy-a young man drowned when a statue fell on him. People gathered at a nearby chai stand to mourn his death. 　Several decades ago, chai was served in small clay pots, known as kulhar in Hindi or bhar in Bengali. While the bowls are still popular in Calcutta, plastic cups, tiny glasses and steel mugs have become the vessels of choice across most Of India.According to the passage, what is commonly used in north Indian chai and thought to be good for health?