a chip that does the computing work—recording things like temperature and motion at its location. Each sensor also has a tiny radio transmitter that allows it to talk to other sensors within 100 feet or so. With a single network of 10,000 sensors—thought to be the biggest array (阵列) of sensors currently possible—you could cover 9 square miles and get information about each point along the way. The data finally works its way to a base station that can send the information to a computer or to a wireless network.
     The scientists who are working with this technology say smart dust sensors can be used to detect the location or movement of enemy troops in areas too dangerous or remote for soldiers to operate. Scattering hundreds of self-networking sensors from a manned or unmanned plane onto the battlefield, in theory, could produce critical information and lead to strategic advantage. Sensors could also be used to detect the presence of chemical weapons and could give troops the time needed to put on protective gear.
41. Smart dust sensors can do all the following EXCEPT ______.
   A. giving troops their protective gear
   B. organizing themselves into a computer network
   C. detecting the movement of military vehicles nearby
   D. operating in remote and dangerous war zones

42. By “physical environment” (Paragraph 2), the writer means such elements as ______.
   A. the position of military troops     
B. the presence of minicomputers
C. the strength of radio signals     
D. the amount of water vapor in the air

43. If connection between two sensors is blocked, the network will automatically ______.
   A. replace the sensor involved     B. repair the sensor involved
   C. ignore the sensor involved     D. destroy the sensor involved

44. To cover an area of 3 square miles and get information about each point along the way, how many smart dust sensors are needed?
     A. About 3,000 sensors.     B. About 3,300 sensors.
     C. About 5,000 sensors.     D. About 6,600 sensors.

45. The passage implies that the smart dust sensors are most likely to be used in ______.
    A. emergency rescue         B. monitoring pollution
     C. military operations     D. evaluating the environment
Passage Four
     Each semester, Andrew Tom receives a term bill outlining his expenses: tuition, dorm fee, student center fee, recreation fee, resident activity fee, health insurance. If only the rest of his expenses were as easy to quantify.
     “It’s like you start out the semester with plenty of money and then $20 for dinner out here and $100 at the department store there, it’s gone,” said Tom, a Northeastern University third-year student. “And there are so many things you need like toothpaste or laundry detergent (洗涤剂) that you don’t think about until you get here and need it.”
     From the books lining their shelves to the fashionable clothes filling their closets, college students say the expenses of a college education go well beyond tuition and a dining hall meal plan. Many say they arrive on campus only to be overwhelmed by unexpected costs from sports fees to the actual price of a slice of pizza.
     Balancing a job with schoolwork, especially at colleges known for their heavy workloads like Harvard and MIT, can be tough. So can the pressure students often feel to financially keep pace with their friends.
     “When you get dragged along shopping, you’re going to spend money; if you get dragged to a party and everyone wants to take a cab but you’re cheap and want to take a bus, chances are you’ll end up sharing the fee for the cab,” said Tom. “I guess you could say no, but no one wants to be the only one eating in the snack bar while your friends are out to dinner.”
     Max Cohen, a biology major at MIT, said he is accustomed to watching fellow students spend $40 a night to have dinner delivered or $50 during a night out at a bar. During the school’s recent spring break, friends on trips for the week posted away messages that read like a world map—Paris, Rome, Tokyo. “Meanwhile I stay home and work,” said Cohen. “I didn’t realize when I came here how much money I would spend or how hard I would have to work to get by.”
     It is a lesson some younger students learn quickly. Others, surrounded by credit card offers, go into deb