A、They can’t talk so they can’t produce any speech. B、They can only produce the sound of "R" at first. C、They can’t discriminate

During the production of speech, when babies listen, what they’re doing is taking statistics on the language that they hear. [22]And what we’ve learned is that babies are sensitive to the statistics, and the statistics of Japanese and English are very, very different. English has a lot of Rs and Ls, while the language of Japanese is totally different. For example, a group of intermediate sounds of English is known as the Japanese "R.". So babies absorb the statistics of the language and it changes their brains; it changes them from the citizens of the world to the culture-bound listeners that we are. But we as adults are no longer absorbing those statistics. We’re governed by the representations in memory that were formed early in development.
    So? what we’re seeing here is changing our models of what the critical period is about. We’re arguing from a mathematical standpoint that the learning of language material may slow down when our distributions stabilize. It’s raising lots of questions about bilingual people. [23]Bilinguals must keep two sets of statistics in mind at once and flip between them, one after the other, depending on who they’re speaking to.
    So we asked ourselves, can the babies take statistics on a brand new language? [24]And we tested this by exposing American babies who’d never heard a second language to Mandarin for the first time during the critical period. We knew that, when monolinguals were tested in Taipei and Seattle on the Mandarin sounds, they showed the same pattern Six to eight months, they’re totally equivalent Two months later, something incredible happens. But the Taiwanese babies are getting better, not the American babies. What we did was expose American babies during this period to Mandarin. It was like having Mandarin relatives come and visit for a month and move into your house and talk to the babies for 12 sessions.
    So what have we done to their little brains? [25]We had to run a control group to make sure that just coming into the laboratory didn’t improve your Mandarin skills. So a group of babies came in and listened to English. And we find that exposure to English didn’t improve their Mandarin. But look at what happened to the babies exposed to Mandarin for 12 sessions. They were as good as the babies in Taiwan who’d been listening for 10-and-a-half months. What it demonstrated is that babies take statistics on a new language. Whatever you put in front of them, they’ll take statistics on.
22. What do we learn about babies’ production of speech?
23. What does the speaker say about the bilingual people?
24. What experiment did the speaker do?
25. What is the speaker’s purpose to run a control group?