21. Read lines 25-26 from the poem.
until everything we think we know
bangs against everything else we know.
The lines help develop a central idea in the poem by suggesting that
A. creative methods for researching particles are frequently being invented.
B. ongoing research continues to add to our knowledge of particles.
C. our understanding of particles is limited by the equipment available to study them.
D. competing theories about particles provoke scientific debate.