In the "dead-ball" era of 1900-1919, Major League Baseball hitters in

OE Magoosh:

Split #1: this is a very tricky "less"/"fewer" split. If we were comparing individual totals of homeruns, something we could count for each person, then we would be comparing something countable, and we would have to used fewer (e.g. "Ted Williams hit fewer homeruns than Reggie Jackson.") Here, though, we are talking about comparing the "average total" --- the average of several seasons is not guaranteed to be a whole number: it could be a decimal. Therefore, we aren't really counting whole things anymore, so we don't used "fewer" (used only for countable nouns), and instead, we use "less." Choices (A) & (B) & (C) have this correct.

Split #2: the comparison. First of all, we don't want to compare the average HR total in the dead ball era to the decade of the 1920s. We need to compare average to average. The phrasing in (C) & (D), "than the 1920s", means we are comparing something to the entire decade of the 1920's ---- this is not what the sentence means. Choices (C) & (D) are incorrect. We are trying to compare the average HR total in the dead ball era to the average HR total in the 1920s. It would be correct to say "than that in the 1920s", because the singular pronoun "that" would be referring the average HR total. BUT, the plural pronoun "those" is not correct: (A) makes this mistake. Only choice (B) correctly drops all the common words ("Major League Baseball hitters in both leagues hit an average total of home runs each season") and economically states just the key words that make the difference: "in the 1920s." This is a remarkably elegant and sophisticated way to convey this comparison, and it is 100% correct. (B) is the only possible answer.