单选题 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.

【正确答案】 B

【答案解析】从“With a single network of 10,000sensors—thought to be the biggest array(阵列) of sensors currently possible—you could cover 9 square miles”可以计算得出选项B。本题是一道很简单的细节题，回原文定位便可以找到答案。