治疗多发性硬化症（）
A．抗CD3单克隆抗体
B．抗肿瘤坏死因子抗体
C．β干扰素
D．α干扰素
E．EPO
参考答案：D
They were surprised that a child should work out the problem____ they themselves could not.
A．once
B．unless
C．while
D．if
