题目内容：
阅读短文，回答题：On a sunny day last August, Tim heard someshouting．Looking out to the sea carefully, he saw a couple of kids in arowboat were being pulled out to sea.
Two 12-year-old boys, Christian and Jack,rowed out a boat to search for a football．Once they'd rowed beyond the calmwaters, a beach umbrella tied to the boat caught the wind and pulled the boatinto open water．The pair panicked and tried to row back to shore．But theywere no match for it and the boat was out of control.
Tim knew it would soon be swallowed by thewaves.
"Everythingwent quiet in my head," Tim recalls(回忆)．"I was trying to figure out how to swim to the boys in astraight line."
Tim took off his clothes and jumped into thewater．Every 500 yards or so, he raised his head to judge his progress． "At one point, I considered turning back," he says．"I wonderedif I was putting my life at risk." After 30 minutes of struggling, he wasclose enough to yell to the boys, "Take down the umbrella!"
Christian mademuch effort to take down the umbrella．Then Tim was able to catch up and climbaboard the boat．He took over rowing, but the waves were almost too strong forhim.
"Let's aim for the pier(码头)," Jack said．Tim turned theboat toward it．Soon afterward, waves crashed over the boat, and it began tosink．"Can you guys swim?" he cried．"A little bit," theboys said.
Once the were inthe water, Tim decided it would he safer and faster for him to pull the boystoward the pier．Christian and Jack were wearing life jackets and floated ontheir backs．Tim swan toward land as water washed over the boys' faces.
“Are we almostthere?" they asked again and again．"Yes," Tim told them eachtime.
After 30minutes,they reached the pier.
Why did thetwo boys go to the sea? A．To go boat rowing.
B．To get back their football.
C．To swim in the open water.
D．To test the umbrella as a sail.
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