自发性气胸出现
A．肺源性呼吸困难B．心源性呼吸困难C．血源性呼吸困难D．中毒性呼吸困难E．神经、精神性呼吸困难
参考答案：A
Pieces of bamboo or wood ________ books between 2nd and 5th century AD.
A. used to formed B. used to form
C. were used to form D. used to beforming
为什么要对钢水进行脱氧？
