Well, we discovered that we needed to upgrade security so that potential criminals weren't coming into our country, and so potentially harmful substances weren't being brought onto our planes. That meant literally anything that could become a bomb, start a fire, stab someone etc. As for Pearl Harbour, I think that had more of an affect on how we thought our military and defence system was working.
Answer:
A, C, and D will be your answers.
"<span>C. The South had more miles of railroad track" is not accurate. Railroads were largely situation going from East to West. It is true that the North had a broader industrial base. </span>
He called the imaginary barrier the "Iron Curtain". He used this image to oppose the Soviet union expansion, and keep in communism in check.
Hope this helps!!!:)