After the first day of fighting at Gettysburg, the arrival of reinforcements allowed ✖ the Union to avoid more casualties.

✔ the Union to hold the line and win.

✖ the Confederacy to break the lines.

✖ the Confederacy time to regroup.

In conclusion, the answer is B.

(I am doing this for the people that come across this question and didn't know the answer.)

{hope this helped}
btw this is a question in the unit test review for grade 7 in the semester a for unit 4.