The pronoun in the sentence is 'they'.
This pronoun repleaces the words 'dogs and cats'.
900Boxer Rebellion in ChinaItaly's King Umberto I AssassinatedKodak Introduces $1 Brownie CamerasMax Planck Formulates Quantum TheorySigmund Freud Publishes The Interpretation of Dreams
1910Boy Scouts Established in U.S.Halley's Comet Makes an AppearanceThe Tango Catches On
1920Bubonic Plague in IndiaFirst Commercial Radio Broadcast AiredHarlem Renaissance BeginsLeague of Nations EstablishedProhibition Begins in the U.S.Pancho Villa RetiresWomen Granted the Right to Vote in U.S.
1930Gandhi's Salt MarchPluto DiscoveredStalin Begins Collectivizing Agriculture in the U.S.S.R.
Hoped this helped
It is A because it’s the only one that really makes-sense
