Answering TOEFL Question No.20 (Task 2)

20. After the children read some stories before they went to bed.

This sentence is incorrect, the correct sentence is :

The children read some stories, before they went to bed.

Analysis : 

Clause 1 : The children read some stories.
Clause 2 : They went to bed.
Clause connector : Before
Subject : The Children
Verb 1 : Read
Verb 2 : Went