单选题 Students learning about how life began on Earth may be presented with the perplexing question, "Which came first, the chicken or the egg?"

【正确答案】 B

【答案解析】perplexing 复杂的，令人困惑的；puzzling 使入迷惑的；pressing 紧迫的； patronizing屈尊俯就的；penetrating敏锐的，有洞察力的。