Question

select the three adjectives. dont select any articles (a, an, or the).
charles kuen kao won the nobel prize in physics in 2009 for groundbreaking work on fiber - optic cables, which use thin threads of glass or plastic to carry information in the form of light.

Explanation:

Adjectives describe nouns. "Groundbreaking" describes "work", "fiber - optic" describes "cables", and "thin" describes "threads".

Answer:

groundbreaking, fiber - optic, thin