How many letters does the top answer for “which of the following carbonated soft drinks were introduced first” have?

The most common answer is dr (2 letters).

Crossword clue: which of the following carbonated soft drinks were introduced first

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

dr 2 letters otdb

pepper 6 letters otdb

attack and bombard with or as if with missiles