A、Because they are better at controlling their attention. B、Because they need to suppress one language to be able to speak in th

In the early 1950s, researchers found that people scored lower on intelligence tests if they spoke more than one language. Research in the 60s found the opposite. Bilingual people scored higher than monolinguals—people who speak only one language.
    The latest evidence shows that being bilingual does not necessarily make people smarter.(4)But researcher Ellen Bialystock says it probably does make you better at certain skills. Bilingual people are often better at controlling their attention— a function called the executive control system.
    Ms. Bialystock says the best method to measure the executive control system is called the Stroop Test. A person is shown words in different colors. "So you would have the word blue written in red, but you have to say red. But blue is so striking, it’s just lighting up all these circuits in your brain, and you really want to say blue. So you need a mechanism to override that so that you can say red. That’s the executive control system."
    Her work shows that bilingual people continually practice this function.(5)They have to, because "both languages are active in their brain at the same time. They need to suppress one to be able to speak in the other.
    This mental exercise might help in other ways, too.(6)Researchers say bilingual children are better able to separate a word from its meaning, and more likely to have friends from different cultures.