The boy didn't feel completely ______ when he was asked to sing a pop song before the whole class.[ ]

A. in surprise  

B. at ease

C. in danger  

D. at present

我国用煤做燃料和用焦炭做燃料冶铁分别开始于

A．汉代、南宋

B．北宋、南宋

C．春秋、汉代

D．北宋、明代