Sugar cube is my answer
Hope this helps!
Let me know if i'm wrong.
The period is the end of the sentence!!!
He used a tube of mercury and marked the height of the mercury when placed in an ice bath as 0 degrees celsius, when he placed the tube in a boiling, he marked the height of mercury and called that 100 degrees celsius, he marked it linearly between 0-100 degrees celsius
I think it’s the third option but I’m not entirely sure