Sherlock Holmes was a world-famous detective who used observation skills to solve crimes.

Which piece of evidence from The Mystery of the Lost Gem best supports this topic sentence?
a
Sherlock Holmes noticed scratches on the floor near the wall.

b
Sherlock Holmes opened the door, and Mrs. Hudson introduced his client.

c
Sherlock Holmes silently vowed that he would find the gem and the thief.

d
Sherlock Holmes was reading by the fire when he heard a knock at the door.