Teacher: In this task, you're given an article and an answer. Your task is to generate the question for the answer based on the given article.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Article: There are a lot of public libraries in Britain. These libraries have more than one hundred and fifteen million books, not including those libraries of public schools. Public libraries not only lend books, music records but also help children, patients in hospitals and others to get special play readings, film shows and so on. The first public libraries were founded in about the year 1850. Today's public libraries usually have a reading-room, a lending room and a reference room. The greatest and most famous library in Britain is that of the British Library in London. It was founded in 1973 and has over 10, 000, 000 books. It has nearly every magazine, newspaper and book published in Britain and other parts across the world.
Answer: 10,000,000 or less.
Solution: How many books are there in the British Library?
Reason: In the Article, 10,000,000 is mentioned for the number of books available in the British Library, so this is a good question.

Now, solve this instance: Article: Babies understand what their mothers say, even when they speak a language their children have never heard before, scientists claim. The researchers found that one-year-olds reacted in exactly same way to their mothers' voices regardless of whether they were speaking English or Greek, showing what mothers have long known - that babies pick up on tone of voice rather than the words themselves. The researchers, from Cardiff University's School of Psychology, observed babies as they watched their mothers perform actions with toys using the English words "whoops" and "there". The scientists studied reactions from one-year-old babies to their mums' voices even when they were speaking both English and Greek, and keeping the same tone of voice. The academics found that babies reproduced the same reactions regardless of whether they knew the language. Study leader Dr Merideth Gattis of Cardiff University's School of Psychology says, "What this work showed was that children could have access to understanding simply through tone of voice. We did 'whoops' and 'there' in two languages and got exactly the same results." The research, published in the journal Cognitive Development, was conducted on 84 babies aged between 14 and 18 months, over the course of a year, with none of the babies having any previous exposure to Greek. Dr Gattis says that children respond to tone clues in their parents' voices from an early age. She says, "Tone of voice is a really useful signal of what someone is thinking. We never have direct access to other people's minds, except the signals in language that they give out." She says the study shows that it is less important what parents say than how they say it. Dr Gattis adds, "A child may ask if you like his / her drawing, for example. You might say yes, but if you don't sound enthusiastic, the meaning may not get across." Before children begin to speak, parents should use exaggerated tone when speaking to them.
Answer: Babies pick up on tone of voice.
Student:
According to the text, what have mothers long-known?