Which sentence has a dependent clause?

Answer:
D. Before he went to sleep he completed his homework.
Explanation:
A dependent clause is a clause that has a subject and a verb, but doesn't make sense on it's own. The dependent clause is"Before he went to sleep", because he is the subject, and sleep is the verb, but doesn't make sense on it's own.
I think it is E. because dependent means on your own. E. says “I” which mean it is him and him only. He is doing it alone. Hope this is helpful :)