Answer the following question given this paragraph: 

Dalton’s theory was soon widely accepted. Most of it is still accepted today. The only part that is no longer accepted is his idea that atoms are the smallest particles. Scientists now know that atoms consist of even smaller particles.


Q: What was once believed to be the smallest of all particles, as dalton's theory proposed?

 Choices:

- nucleus

- molecule

- neutron

- atom

A:
atom
