题目内容：

阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。

If you enjoy kayaking (皮划艇运动), you can paddle for free in Denmanrk, Ireland, Germany, Sweden and Norway, but you also have to be willing to pick up trash.

Organized by Greenkayak, free trips in the group's two-person kayaks are offered in return 1.collecting waste from water surface. 2.project began in Demark in April, 2017. With the help of a thousand kayak 3.(voluntary), three tons of trash were collected from Copenhagen harbor that year. You can easily book a kayak for the time 4.works for you. Life jackets and equipment — like a paddle, a waste picker, a bucket for the trash —5. (provide): just bring yourself. You can have two hours of free kayak time.

Greenkayak believes that kayaks are highly effective at collecting waste because they can get close to areas that are otherwise hard 6.(reach).

“In Denmark, people love to hang out on canals, but 7.(fortunate) they see waste 8. (float) by.” one of Greenkayak's co-founders speaks of the program's origin. “You can't take your shirt off and jump in. 9. you can get in a Greenkayak and make a difference.”

If you want to take advantage of the free kayak, 10.(tourist) a city from its river and do your part to control water pollution.