The most extreme objects in the universe tend to put on spectacles. When a giant star (46)            as a supernova, it can outshine its own galaxy as it dishes out heat, X-rays, and the highest energy radiation of all, gamma rays. So when NASA launched a gamma-ray telescope into space in 2008, astronomers figured the high-energy radiation it (47)            would point the anway to easily identifiable supernova remnants, black holes and other extroverted objects.

They couldn't have been more wrong. Last January, after a (48)            survey, scientists with the Fermi Gamma-ray Space Telescope released a list of nearly 500 locations where the spacecraft detected the highest-energy gamma rays. More than a third of them cannot be linked to any known astronomical object. The 169 mystery sources might be previously undiscovered supernova remnants or black holes, or they could be a completely new type of super powerful object. For now, they are total enigmas. “These are the dogs that don't bark,” NASA astrophysicist David Thompson says.

Astronomers are starting out with the simple explanation that they overlooked these objects in previous surveys. They are analyzing X-ray, optical, radio, and infrared (49)            of the hot spots to see if they missed something. But Thompson hopes the answers are more (50)           . The gamma rays might be a byproduct of decaying clumps of invisible dark matter, he says, or of something unknown. “That's what we're really interested in. Not just more of the same, but new types of systems.”

• 46.
  • a. escalates
  • b. explodes
  • c. emits
  • d. entropy
• 47.
  • a. emitted
  • b. leaked
  • c. detected
  • d. expended
• 48.
  • a three-years sky
  • b. three-year sky
  • c. three-year-sky
  • d. three-years-sky
• 49.
  • a. sounds
  • b movies
  • c. graphs
  • d. images
• 50.
  • a. terrifying
  • b. unable
  • c. exotic
  • d. conservative

Deep in the frozen tundra of north-eastern Siberia, a squirrel buried fruits some 32,000 years (51)            from a plant that bore white flowers. This winter a team of Russian scientists announced that they had unearthed the fruit and brought tissue from it back to (52)           . The fruits are about 30,000 years older than the Israeli date palm seed that previously held the record as the oldest tissue to give life to healthy plants.

The researchers were studying ancient soil composition in an exposed Siberian riverbank in 1995 when they discovered the first of 70 fossilized Ice Age squirrel burrows, some of (53)            stored up to 800,000 seeds and fruits. Permafrost had preserved tissue from one species - a narrow-leafed campion plant - exceptionally well, so researchers at the Russian Academy of Sciences recently decided to culture the cells to see if they would grow. Team leader Svetlana Yashina re-created Siberian (54)            in the lab and watched as the refrigerated tissue sprouted buds that developed into 36 flowering plants (55)            weeks.

This summer Yashina's team plans to revisit the tundra to search for even older burrows and seeds.

• 51.
  • a. before
  • b. since
  • c. ago
  • d. from
• 52.
  • a. earth
  • b. home
  • c. basics
  • d. life
• 53.
  • a. whom
  • b. whose
  • c. who
  • d. which
• 54.
  • a. conditions
  • b. heat
  • c. posture
  • d. fashion
• 55.
  • a. from
  • b. within
  • c. since
  • d. by