The students entered the classroom, smiling and ___, and ___ down to have their lessons.

A． talked; sat

B． talking; sitting

C． talking; sat

D． talked; sitting

食品卫生与身体健康密切相关．下列做法对人体健康有害的是（　　）

A．用工业石蜡给大米上蜡“美容”

B．蒸馒头时加入适量小苏打

C．用食醋作食品的调味剂

D．用活性炭作自来水净水剂