TOEFL Reading: ETS-TOEFL阅读机经 - Y32S5QJEE4AE7W6OL$

The phrase "special exchange" in the passage refers to A. the transfer of cellulose digesters from one colony of termites to another B. the development of small colonies into much larger ones C. the transfer of liquid secretions from adult termites to young termites D. the departure of certain reproductive termites and the arrival of others