根据短文意思，在41～50各题的空格里填入一个恰当的词语，使句子通顷、完整。
Long, long ago, people didn't have telephones 1_____ other modern ways to send messages to others,
but they still could send messages 2_____ many different ways. A man put his ear to the ground. 3_____
he heard the sound of the horses, he quickly ran to tell his people. He was a runner. That was one way
to send messages.
People 4_____ sent messages by smoke. One man made a cloud of smoke. In the next place people
saw the smoke and went on doing that, too. The message thus went from one place 5_____ another by
smoke.
Much later, some soldiers kept many pigeons (鸽子). These pigeons always flew back. When a soldier
was sent far 6_____ from his place, he might carry 7_____ pigeon with him. He could write a message
8_____ put it on the bird's leg. 9_____ would fly back with the soldier's message.
These are some ways to send messages. 10_____ you think of some faster ways?