Directions: Complet the following passage by filling in each blank with one word that best fits the context.
When very small dinosaur bones were found in a Germany mine people thought they were from baby dinosaurs.   48  , scientist Martin Sander's work shows that they were probably fully grown and belong to the smallest giant dinosaur species ever found.
Growth marks on dinosaur bones are similar   49   growth rings on trees. The rings are far apart while the animal is young and growing quickly.  50  get closer as growth slows. "It is exactly these tight ring marks that we found in the fossil (化石) bones," says Sander. So the fossils must have been from adult animals. 
51  was this German dinosaur so much smaller than other giant dinosaurs, which grew up to 45 metres long and weighed as much as a thousand humans?
150 million years ago, most of Germany was underwater. Scientists think that  52  water levels rose, there was less and less land and food available. The dinosaur was forced to adapt and evolved into  53  smaller animal needing  54  space and food.
Since 1998, scientists have dug up more than 1,000 dinosaur fossils in the mine. It is one of the few places in the world  55  the bones and footprints of dinosaurs have been found together.