has/have a bad effect on sb./sth.对什么人或事物有坏影响.
1）Haven’t you noticed that you have become smarter since you started to learn a language?
2）According to a new study by a British university,learning a second language can lead to an increase in your brain power
3）The study also found the effect is greater,the younger people learn a second language.
4）It means that the change itself increases the ability to learn．
5）The results showed,that the younger they started to learn,the better．
以上句子可以看出学习“二外”是有好处的,而不是“bad”.