The correct answer is: "After we considered all the disagreements, we abandoned the proposal."
A dependent clause is a group of words with a subject and a verb. Furthermore, it cannot stand alone. As you can see, the clause "we considered all the disagreement" has the subject(we) and a verb(considered). However, if we put "after" before that clause, it cannot give you the complete meaning; hence, it is a dependent clause. All the other options contains either fragments or other grammatical errors.
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