Answer:
when u find the right one
What is wrong in this sentence is the pronoun their.
As you can see, the pronoun <em>their </em>in this sentence refers to <em>the modern American family. </em>Since the word <em>family </em>is singular, the pronoun which modifies it also has to be singular. So, instead of using the pronoun <em>their, </em>it should be <em></em><u>its.</u>
I believe the answer is sentence 1 hope this helps :)