Answer:
Critical versus Sensitive Periods
Explanation:
In the critical period of a child's development the if certain things are not learnt it becomes almost impossible to learn them at a later stage in life.
According to certain scientists it is believed that if things are not learnt at a particular stage then it becomes difficult but possible to learn.
Here, the learning of a language is being studied. It is true that learning a language when you are a child is easy but it is difficult to learn a language after a certain.
Hence, the key issue that is being highlighted here is Critical versus Sensitive Periods.
