资料题：According to the speaker, why did Hudson River sloops have tall masts（　）。

The Hudson River has a couple of interesting physical features that made it very attractive for settlement by the Europeans.The first is that the river extends inland from the Atlantic Ocean for mare than 150 miles with mo waterfalls or rapids.Is surface is virtually flat for that entire distance with no obstacles.Second, the whale 150 -mile stretch is influenced by tides from the Atlantic Ocean.Roughly every six hours the river reverses direction, flowing north when the tide is rising and south toward the ocean when the tide is going down.Obviously there were no obstacles to prevent settlers from moving further upstream on the Hudson River.And this explains why the Dutch penetrated so far inland.They were the first Europeans to settle in the Hudson Valley.Of course, to go upstream the Dutch settlers needed the right kind of boat and so to navigate the river, they designed a sloop(单桅帆船) with only one mast but with two sails,one rigged in front of the mast and one behind.The mast was very tall, in many cases, over 100 feet tall so that the large sails could catch winds blowing above the shoreline hills.Hudson River sloops carried passengers and cargo, the cargo ranging from coal, lumber and hay to fruit, vegetables and livestock.Traveling only 10 miles an hour in a good wind, he sloop was not too speedy by modem standard, but it was ideally suited to the Dutch settlement, and, in fact, when the steamboat eventually was introduced, it couldn't keep up with the sloop.