Booth was surprised upon entering the president's box because...

• A. Lincoln greeted him warmly
• B. There was no guard at the door; Charles Forbes sat near the door
• C. The box was empty
• D. A soldier stood at the door

Answer: (B)

Booth’s surprise rests on a security slip at Ford’s Theatre. There was no guard stationed at the door, so he could slip into the president’s box without being challenged. Charles Forbes sat near the door, providing a nearby presence that didn’t raise alarms and helped mask Booth’s approach. With the entrance left unguarded and a nearby observer not signaling trouble, Booth could move in quietly and catch Lincoln off guard. This setup fits what happened, whereas the other ideas would imply more active security or a different scene than the one described.