The answer is B.
The smallest scrap of debris after cleaning up is Fragment.
Blob - a very small round mass of liquid or sticky substance.
Fragment - a small piece of something that has broken off or that comes from something larger. The road was covered with fragments of glass from the shattered window.
Glimmer - a small amount, a slight sign.
Speck - a very small mark, spot, or piece, or amount of something.