Extra

Unit 2, Listening, Activiti 4

In the question 5 says: What do some psychologists belive is likely to increase the "birth arden effect?

The answer of Max is having siblings of the same sex, and I  belive that is true this sentence, because, siblings of the same sex, among them are more competives, so yes, if ther ages are very close.
In my opinion, if ther ages aren't very close, the effect is weaker.