According to the information in the third paragraph, which of the following improvements made it possible to lengthen the tone produced by the piano?()
Why does the author mention electric eels?
How many volts of electricity can an electric eel emit?
It can be inferred from the passage that the longer an eel is the
【单选】
What does the passage mainly discuss?()
Which of the following instruments was widely used before the seventeenth century?()