Answer:
'I managed to complete the task, but I missed the deadline.'
Explanation:
A compound sentence is a sentence with two or more independent clauses.
'I managed to complete the task.' is an independent clauses and sounds normal alone.
'I missed the deadline.' is also an independent clauses and also sounds fine alone.
The second and fourth answer don't even look like they would be a compound sentence because the second sentence is a complex sentence and the fourth is a simple one.
The second one is a complex sentence because it has one independent clause and one dependent one.
The fourth sentence is a simple one because it only has one clause, which is independent, if it weren't, it'd be a fragment sentence.
The third answer/sentence looks like it could be a compound sentence, but if we look closer, it's also a complex sentence because the first part of it is dependent, not independent.
