[单项选择]哪个不是吡拉西坦的特点（）
A. 具五元杂环内酰胺结构
B. 对重度痴呆无效
C. 属于γ-氨基丁酸的环状衍生物
D. 是乙酰胆碱酯酶抑制剂
E. 其中枢兴奋作用弱副作用小

D

Nearly 5,000 years ago, during the Late Stone Age, people began building Stonehenge. It became a long-term project. People added to the site for more than 1,500 years. Most likely Stonehenge was first built as a place to hold religious rituals (仪式) and bury the dead. But experts (家) are not sure because there are no written records telling us what took place at Stonehenge.
At first the site was just a circular ditch (沟渠). Within the circle were two burial hills, and a smaller circle of 56 holes. Scientists have found ashes in the holes. They believed these are from the burning of the dead bodies.
But Stonehenge may have been more than a ritual site. Some experts suggest it was also used as a huge calendar (日历) for watching stars. Outside the entrance of the construction stands the Heel Stone. On the summer solstice, the longest day of the year, a person standing at the center of the circle can look out through the entrance and see the
A. 选项A
B. 选项B
C. 选项C
D. 选项D