Answer:
A. frustration that McClellan had amassed and trained a huge military force but refused to use it to attack the Confederates.
Step-by-step explanation:
George B. McClellan was an alumni of the United States Military Academy who fought in the Mexican War and led several expeditions. He was considered as a distinguished soldier with great personality traits.
He established and commanded a strong army force that helped the Union win the Civil War. However, during the initial period of the war, McClellan portrayed reluctance and unwillingness to take orders from anyone.
President Lincoln was frustrated that McClellan had amassed and trained a huge military force but refused to use it to attack the Confederates.
Therefore, President Lincoln remarked early in the Civil War that he would like to borrow General McClellan's army if he does not want to use the army.