What type of GPS system downloads data through a land-line phone at night?

The correct answer is passive GPS system. A passive GPS system is designed to collect and store data for later download, typically through a land-line phone or other means. This type of system is often programmed to retrieve the data at specific times, such as during the night when the user is less likely to be moving around. This functionality allows for the tracking of an individual's whereabouts without them being constantly monitored in real-time, which is a notable feature of passive systems.

In contrast, active GPS systems provide real-time tracking by continuously transmitting data to a monitoring center. Electronic systems refer to the broader category of technology used in surveillance and monitoring but do not specifically target the type of data download method. Continuous systems generally imply ongoing tracking without breaks, which aligns more closely with active systems rather than the periodic downloading characteristic of passive systems. Thus, the defining feature of a passive GPS system is its method of data collection and transfer, which makes it the correct choice in this context.