听力原文： Early one morning, more than a hundred years ago, an American inventor called Elias Howe finally fell asleep. He had been working all night on the design of a sewing machine but he had run into a very difficult problem; (29)it seemed impossible to get the thread to run smoothly around the needle. Though he was tired, Howe so, Howe ran into the salve problem as before. (29)The thread kept getting caught, around the needle. The king flew into the cage and ordered his soldiers to kill Howe. They came up towards him with their spears raised, hut suddenly the inventor noticed something. There was a hole in the tip of each spear. The inventor awoke from the dream, realizing that (30)he bad just found the answer to the problem. Instead of trying to get the thread to run around the needle, he should make it run through a small hole in the center of the needle. This was the simple idea that finally made Howe design and build the first really practiced sewing machine．(31)Elias Howe was not the only one who found the answer to his problem in this way. Thomas Edison, the inventor of the electric light, said his best ideas came into him in dreams. So did the great physicist Albert Einstein. Charlotte Bronte also drew in her dreams in writing Jane Eyre.
(30)

A. What kind of thread to use.
B. How to design a needle which would not break.
C. Where to put the needle.
D. How to prevent the thread from getting caught around the needle.