Read each sentence to find out whether there is any error in it. The error, if any, will be in one part of the sentence. The number of that part is the answer. Since the husband and wife / could not solve their differences, / the court stepped / in to do it.

The error is in part 4. When 'in' is part of the infinitive verb 'to do', it should not be separated from 'to' - it should be 'into do it' (one word) not 'in to do it'. The phrasing 'stepped in to do it' incorrectly treats 'in' as a separate word when it should be the preposition 'into'. Parts 1, 2, and 3 are grammatically correct.