Question

read the passage.
finding the invisible
all over the planet, ancient tombs and temples lie hidden from view. so how do archaeologists know where to begin digging? thanks to satellites, that question is becoming easier to answer. in the pioneering field of satellite archaeology, satellites four hundred miles above earth can identify structures buried under soil, covered by modern construction, or obscured by forests. for example, mud bricks used by ancient egyptians are more dense than soil, and the differences are detected by the satellites. advanced computer programs map buried settlements and distinguish them from water, vegetation, and farmland. sarah parcak, a pioneer in the field, says of the technology, \it allows you to literally strip away vegetation and see entire cities beneath the rain forest canopy. this is the unbelievable future of archaeology.\
what is the main, or central, idea of the passage?
archaeologists must determine where ancient structures are buried before they can begin excavating them.
archaeologists are uncovering ancient hidden structures by using satellite imagery.
satellite archaeology is a rapidly expanding new scientific field.

Explanation:

To find the main idea, we analyze each option:

• The first option ("Archaeologists must determine where ancient structures are buried before they can begin excavating them") is a general statement about archaeologists' need to find sites, but it doesn't focus on the satellite technology discussed in the passage.
• The second option ("Archaeologists are uncovering ancient hidden structures by using satellite imagery") matches the passage's content, as the passage explains how satellites help archaeologists identify buried/obscured ancient structures (like tombs, temples) and gives examples of how this technology works (e.g., detecting dense mud bricks, mapping settlements).
• The third option ("Satellite archaeology is a rapidly expanding new scientific field") is not supported by the passage, which focuses on how satellite technology is used to find ancient structures, not on the field's expansion rate.

Answer:

Archaeologists are uncovering ancient hidden structures by using satellite imagery.