根据短文内容，完成下列小题。

    Canadian Geese are large blue and white birds. When autumn comes, they have to fly south where the weather is warmer. The winters are so cold in Canada that the birds will die if they stay there.

    Last spring, Bill Lishman found sixteen young Canadian Geese on his farm. They had lost their parents. Bill thought, "These young birds won't know what to do in the autumn." He had a small plane and he decided to teach the birds to follow him. All through the summer, he went on short trips in his plane and the young geese flew after him.

    When the cold weather arrived in the autumn, Bill flew to Virginia in the United States, 600 miles south of his home in Canada. The geese followed him all the way. Bill left the geese in Virginia and he returned home.

    This spring, Bill was waiting for the birds to come back. They didn't arrive, so Bill flew to Virginia to get them. He looked for them for two weeks, but he couldn't find them. When he arrived back home, he found the geese waiting for him. They had found their way home without him!

把10克盐溶在40克水中，盐的重量是盐水重量的（  ）

为了探究声音是怎样传播的，小丽同学用如图所示的装置进行探索．把正在发声的电铃放在玻璃罩内，电铃和罩的底座之间垫上软的泡沫塑料．逐渐抽出罩内的空气，她听到的电铃声音逐渐变小，这种现象表明声音不能在____ 中传播。在做实验时虽然听到的铃声逐渐变小，但始终都能听到铃声，请你分析原因可能是：____ 。