Read the source given below and answer the question that follows:

In the hundred years between 1450 and 1550, printing presses were set up in most countries of Europe. Printers from Germany travelled to other countries, seeking work and helping start new presses. As the number of printing presses grew, book production boomed. The second half of the fifteenth century saw 20 million copies of printed books flooding European markets. The number went up in the sixteenth century to about 200 million copies. This shift from hand printing to mechanical printing led to the print revolution.

[[1]] millions of copies of printed books flooded the markets of Europe in the second half of the fifteenth century.