LONDON(Reuters)--Quiet please--Britain's Queen Elizabeth is preparing to have her swans counted. Buckingham Palace has announced that the annual Swan Upping, a tradition dating back to the 12th century which involves a counting of the swan population on the River Thames, will be conducted by the Queen's official Swan Marker from July 20 to July 24. "With the assistance of the Queen's Swan Warden, Professor Christopher Perrins of the University of Oxford, the swans and young cygnets   are also assessed for any signs of injury or disease," Buckingham Palace said in announcing the count. The process involves the Swan Marker, David Barber, rowing up the Thames for five days with the Swan Warden in traditional wooden boats while wearing special scarlet uniforms and counting, weighing and measuring swans and cygnets. It may seem strange, but it is very important to the Queen. According to custom, Britain's queen or king owns all unmarked, mute   swans in open water, but the Queen now exercises the right only on areas of the Thames and its nearby  _  In medieval   times, the Swan Marker would not only travel up the river counting the swans, but would catch as many as possible as they were sought after for banquets and feasts. This year, the Swan Marker and the Swan Warden are particularly keen to discover how much damage is being caused to swans and cygnets by attacks from dogs and from  abandoned fishing tackle  . It is also an important year because Queen Elizabeth has decided to join her team of Swan Uppers for part of the census. She will follow them up the river and visit a local school project on the whole subject of swans, cygnets and the Thames. "Education and conservation are essential to the role of Swan Upping and the involvement of school children is always a rewarding experience," Buckingham Palace said. We can infer from the passage that the process of counting the swans   _  .
remains almost unchanged in the past years involves a lot of royal members sometimes lasts longer than before is always guarded by special soldiers
Question: LONDON(Reuters)--Quiet please--Britain's Queen Elizabeth is preparing to have her swans counted. Buckingham Palace has announced that the annual Swan Upping, a tradition dating back to the 12th century which involves a counting of the swan population on the River Thames, will be conducted by the Queen's official Swan Marker from July 20 to July 24. "With the assistance of the Queen's Swan Warden, Professor Christopher Perrins of the University of Oxford, the swans and young cygnets   are also assessed for any signs of injury or disease," Buckingham Palace said in announcing the count. The process involves the Swan Marker, David Barber, rowing up the Thames for five days with the Swan Warden in traditional wooden boats while wearing special scarlet uniforms and counting, weighing and measuring swans and cygnets. It may seem strange, but it is very important to the Queen. According to custom, Britain's queen or king owns all unmarked, mute   swans in open water, but the Queen now exercises the right only on areas of the Thames and its nearby  _  In medieval   times, the Swan Marker would not only travel up the river counting the swans, but would catch as many as possible as they were sought after for banquets and feasts. This year, the Swan Marker and the Swan Warden are particularly keen to discover how much damage is being caused to swans and cygnets by attacks from dogs and from  abandoned fishing tackle  . It is also an important year because Queen Elizabeth has decided to join her team of Swan Uppers for part of the census. She will follow them up the river and visit a local school project on the whole subject of swans, cygnets and the Thames. "Education and conservation are essential to the role of Swan Upping and the involvement of school children is always a rewarding experience," Buckingham Palace said. We can infer from the passage that the process of counting the swans   _  .
A. remains almost unchanged in the past years
B. involves a lot of royal members
C. sometimes lasts longer than before
D. is always guarded by special soldiers
Answer: