Conjunctions are words used to connect clauses or sentences. They help to establish relationships between ideas and provide coherence to the overall meaning of a sentence. In this case, we need to choose the correct conjunction to connect the clauses "Read over your answers" and "correct all mistakes before you pass them up."

The correct conjunction in this case is "and."

Explanation:
- "And" is a coordinating conjunction that is used to connect two independent clauses when the ideas expressed in those clauses are related or complementary to each other. It indicates that both actions should be performed in sequence.
- In this sentence, the first clause is "Read over your answers," which means to review or examine the answers you have written.
- The second clause is "correct all mistakes before you pass them up," which means to identify and rectify any errors or inaccuracies in the answers before submitting them.
- By using the conjunction "and" between these two clauses, the sentence suggests that both actions should be carried out together, emphasizing the importance of reviewing and correcting mistakes before submitting the answers.

Other options:
- "So" (option A) is a coordinating conjunction used to indicate a consequence or result. It does not fit in this sentence because it does not establish a clear relationship between the two clauses.
- "For" (option B) is a subordinating conjunction used to introduce a reason or purpose. It does not fit in this sentence because it does not connect the clauses in a way that shows their relationship.
- "But" (option D) is a coordinating conjunction used to show a contrast or contradiction between two ideas. It does not fit in this sentence because there is no opposition or contradiction between the actions of reading over the answers and correcting the mistakes.

The correct conjunction to fill in the blank is "and." Here's the detailed explanation:
- The sentence structure indicates that the missing conjunction should connect two related actions.
- The first action is to "read over your answers."
- The second action is to "correct all mistakes before you pass them up."
- Both actions are necessary and should be done in sequence.
- The conjunction "and" is used to connect two actions that are performed one after the other.
- "And" indicates that both actions are equally important and should be completed together.
- It shows that the reader should not only read over their answers but also correct any mistakes before submitting them.
- The conjunction "so" suggests a cause-and-effect relationship, which doesn't fit the context of the sentence.
- The conjunction "for" is used to indicate a reason or purpose, which doesn't fit the context either.
- The conjunction "but" is used to contrast ideas, which is not appropriate here.
Therefore, the correct conjunction to fill in the blank is "and."