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Use a, the or zero article to fill in the gaps. On its way to (1) ... near-Earth asteroid, (2)... spacecraft late last month took some 500 snapshots of a tiny rock called 431 Mathilde. After viewing (3)... images, which depict (4)... battered rock pitted with (5)... craters, planetary scientists had one key question: Why does this asteroid still exist? (6)... craft, known as NEAR (near-Earth asteroid rendezvous), spied five craters more than 20 kilometers in diameter gouged into (7)... sunlit side of Mathilde which is about 50 km across. This rock has been through collisional hell,quot; says Joseph Veverka of Cornell University, yet its surface indicates it has survived for at least 2 billion years. An initial analysis of radio wave observations suggests (8)... possible explanation. (9)... data indicates that the dark rock has (10)... low density, like that of (11)... pile of sand loosely bound by (12)... gravity. When (13)... object strikes such a body, notes Veverka, its like hitting a sponge.quot; Rather than shattering Mathilde, (14)... shock wave from (15)... impact may be absorbed (всасывать).