Electrons, protons and which other sub-atomic particle were discovered in the 19th and early 20th century?

The electron, discovered in 1897 by J. J. Thomson, was the first subatomic particle to be observed. The nucleus of ordinary hydrogen was understood to be a single proton after the nucleus of the atom was discovered in 1911 by Ernest Rutherford. In 1932, a neutron was detected.

can you attach a picture of the lettuce? : )

where are the choice options?