Read the following excerpt from The Mystery of the Disappearing Thief. Sherlock Holmes listened to the tale and agreed to visit the crime scene. The safe was open and empty, but it was not damaged. There was no visible entry into the room where the safe was kept: the windows were sealed, and the door was not damaged. Mrs. Blakely led Sherlock Holmes farther into the house and stopped in the middle of a hallway of old portraits. There were no windows, and the only door was at the other end of the hallway.

"This spot is where I found the black mask," Mrs. Blakely explained.

Sherlock Holmes inspected the hallway with a wrinkled brow. He walked up and down the hallway. He put his hand on the smooth floor. Then, Sherlock's brow smoothed and a glint entered his eyes. Turning to the wall, he pressed the expensive portrait into the wall.

"What are you doing to my painting?" Mrs. Blakely gasped.

Read these sentences from the passage.

Sherlock Holmes inspected the hallway with a wrinkled brow. He walked up and down the hallway. He put his hand on the smooth floor. Then, Sherlock's brow smoothed and a glint entered his eyes.

What do these sentences show about Sherlock Holmes' thoughts in this moment? (2 points)

a
He is concerned that the mystery is too difficult for him to solve.

b
He is perplexed at first, but then he thinks he has the answer.

c
He is unsure where to look for clues.

d
He thinks Mrs. Blakely is the thief.