(一)
David knew the waterfall was coming.It wasn't his first visit to the river in central California.He figured he would hop out of his raft into the shallow water，rappel down the rocks(沿岩壁绕绳下降)on either side of the falls，and continue on his way，as he had on a previous trip.
But this year was different.Heavy snow and spring rains had turned the usually manageable falls into something fierce.And this year，instead of his friends，David's companions were his wife，Sara，and his 13yearold son，Hunter.As the three of them approached the falls late on the afternoon of the third day of their camping trip，David could tell from the increasing roar of water in the narrowing valley that they were in serious trouble.There was no way they'd be able to rappel down the rocks as planned.
They could wade(蹚水)to the shore，but would anyone find them there？They had no phone service，and they hadn't seen a single person in the past three days.And David knew they'd be sharing the ground there with snakes and mountain lions.
As he wondered what to do，David had a bit of luck—he heard voices coming from the other side of the falls.He yelled，but the sound of the rushing water drowned him out.
“We have to get these people a message，” David thought.He caught a stick and pulled out his pocketknife to carve “Help” in it.Then he tied a rope to it so the people would know it wasn't just any stick.He tried flying it over the falls，but it floated away in the wrong direction.
Then he spotted his green water bottle.David grabbed it and carved “Help！” on it.Sara also reminded him that he had a pen and paper，which she'd brought to play games with，in his backpack.
David knew it was just an attempt.But he wrote down “61519 We are stuck here at the waterfall.Get help please” and pushed the note into the bottle.
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This time，his throw over the waterfall was perfect.______________________________
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The next morning，they heard a helicopter hovering(盘旋)above them.______________
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[参考范文]
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This time，his throw over the waterfall was perfect.“All right，that's all we can do，” David said.It took 30 minutes to navigate back upstream to the beach where they'd had lunch.They made a fire and as the evening wore on，they waited for rescue anxiously.By about 10：30 p．m.，they decided they probably weren't going to get rescued that night，so they pulled out their sleeping bags.Before turning in，Sara added more wood to the fire to keep the mountain lions away.
