My guest for today is Paddy Robertson. He and I met on his first night in Beijing, about a year and a half ago. At the time, he was just beginning to study Chinese, and now he speaks the language far better than most foreigners, even among those who have been here for much longer than him. How has Paddy managed to learn Chinese so quickly? One big reason is that he works for Smart Air, which sells affordable air purifiers. His co-workers are Chinese, so he gets to practice the language on a daily basis.