TOEFL Reading: ETS-TOEFL阅读机经 - U4MDEF6441C43H3WL$

According to paragraph 3, how did sanitation problems in early farming societies lead to the spread of infectious diseases? A. Water used for irrigation crops was not always clean. B. Larger populations were increasingly exposed to human and animal waste. C. Farm products that spoiled in fields attracted insects and animals with diseases. D. Lack of varied food sources occasionally forced communities to eat food that carried diseases.