Whether you're heading into the wild or down the road, it's hard to find a better electronic sidekick than a GPS. (Well, you know, other than a cell phone.) Because a GPS has to receive a signal from space, physical impediments(遮挡) like skyscrapers, cliff faces, and even trees can stump(阻断) it. Reception is less of an issue with the ultrasensitive(超灵敏) chipsets in newer models, but if the walls are closing in on you, take a tip from a time when navigation systems weren't the streamlined panels they are today: Hooking up an antenna(天线) will make use of even the most tenuous celestial connection. There's a port on the back of most GPS devices for jacking in. You'll also want to remember that a GPS is not a compass: It runs on software. Like your PC, it needs to communicate with the mother ship periodically. Vendors(供应商) refresh firmware and maps on a regular basis, sometimes even daily. These updates deliver new bits of data that significantly affect your gadget's accuracy. But if you live in the boonies(郊区) on a road named after your sister-wife, don't expect NavTeq to come a-knocking with its survey equipment. Fortunately, most companies make it easy to update your own maps. Usually it's as simple as plugging into your home computer, dropping a couple of pins in Google Maps, and clicking Save. If you own a new Tom Tom, it's even easier. You can edit maps on the unit itself, though you might not have to: Some of the company's navigation updates themselves. Tom Tom's IQ Routes software takes data from every person who uses the company' gadgets and readjusts its assumptions about which roads you should use and how long a given route will take. It will even change its own maps. See, it's not that hard: Your GPS may use NASA technology, but getting the most out of it isn't rocket science. 46. The writer thinks the useful electronic partner is __ ____besides a cell phone when driving outdoors. A. a GPS            B. Tom Tom's IQ Routes              C. a PC       D. NASA 47. Which statement is NOT true about a GPS according to the passage? A. It receives a signal from space. B. It is not a compass. C. It needs to refresh its information. D. It has no port to connect other equipment. 48. You may learn from the passage that Tom Tom (Para 4) is _______. A. a GPS receiver B. a device that can be used to edit maps C. a device that can be used to update software D. a person who readjusts GPS assumptions 49. The main idea of the last paragraph is _______. A. that we should make the most of GPS in rocket science B. that getting the most out of GPS is too difficult C. getting the most out of GPS is very easy D. GPS owns NASA technology 50. Which is not mentioned about a GPS according to the passage? A. Its usage.          B. Its price and shape.   C. Its technology.     D. Its benefit.