Exactly what is the nexus theory? The necessity to gather and remit US sales tax is rooted within the theory of ?�nexus?? which can be a ??connection??to a particular condition and so its oblique tax principles.|默�??�况下，?�供?�天气情?�是美国?�，?�以你必须?�己?�它?�动?�改?�中?�的?�市?�如?�