 | It's located at the western gate, just beside the ticket center. The center provides a series of services, such as guide service, free water supply, guide books, charging mobile phones, baby carriage, first-aid medicine, and simple health care. You can also buy some souvenirs like stamps, postcards and tiger toys.
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 | It's located at the eastern and western gates of the Pearl Spring Scenic Area. There are all kinds of tickets, such as tickets for the scenic area and tickets for amusement park.
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 | Dingshan Pavilion Dining Hall, a large-scale dining centre, can receive 300 people for dining at the same time. It lies in the Scenic Area. Tourists can enjoy the beautiful scenery while eating. It's open from 8 a.m. to 8 p.m. every day.
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| You can take No. 168 bus from Gulou Bus Stop and get off at Pearl Spring Bus Stop. The bus stop is just outside the Scenic Area. You can also drive here. |
.设该圆过点（3，5）的两条弦分别为AC和BD，且
.则四边形ABCD的面积最大值为（ ）
