题目内容：
根据以下材料，回答题This is the most exciting kayaking expedition possible for beginners. You can expect to experience a whole range of different conditions and scenery. This expedition is a total of 8.27 km in distance and it actual-ly enters the streams in the North of Ubin and exits in the South.
Three and a half kilometers of pure mangroves (红树林)makes this the longest pure mangrove kayaking expedition in Singapore. The distance spent inside the mangrove gives you the maximum opportunity to wit-ness wildlife within the mangrove ecosystem. Come experience the challenge of operating your kayak through the labyrinth (迷宫)of waterways and be amazed at the calm and quiet beauty of the wetlands. This last cor-ner of natural wilderness in Singapore is so inaccessible that very, very few have ever experience it--which makes this a truly special program.
Most Recent Travelers' Reviews
Traveler A : Traveled from bottom to top of Singapore in rush hour traffic in order to get to Ubin for a 9:30 start--only to find no guide there. Although, once he arrived, the guide was lovely--offering a very knowledgeable tour and lots of enthusiasm around a beautiful part of the world--our 6-hour kayaking trip was actually over before 2:30 pm, despite only hitting the water at 12 noon.
Traveler B : The guides were nice,however the biggest disappointment was the timing. We thought we were going fora 4-hour kayak but were back in 2 hours and that included the pre-kayak safety talk. The man-groves are lovely but we were told that a storm was near. We felt that there had never been any intention of going out for longer.
( ) What is special about the kayaking trip for travelers is that they_______. A．have a good relaxation by kayaking
B．feel the challenge of kayaking
C．enjoy the beauty of the wetlands
D．experience the wonder of mangroves
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