For many centuries, our understanding of atoms didn't change very much from that of the ancient Greeks. In 530 BC the Greek philosopher Democritus wrote that atoms moved around in a void bouncing off each other or attaching to each other. The word "atom" comes from the Greek a-tomos which means "cannot be divided." Atoms were considered the smallest things in existence. It wasn't until the 19th century that these ideas began to be challenged by scientists such as J.J. Thomson, John Dalton, and Ernest Rutherford. Thanks to these scientists and others, our understanding of the atom is more complex than it ever was, and it continues to evolve and change. For example we now know that atoms are not the smallest things in the universe, and that atoms are made up of even smaller elements such as protons, neutrons, and electrons. Which best describes the author's attitude in the passage? 1. frustrated, because our understanding of the atom is so limited 2 smug, because our understanding of the atom has progressed significantly 3. hopeful, because our understanding of the atom is advancing 4 satisfied, because our understanding of the atom is complete​