金属导电是由带 电的 定向移动形成的。
负；自由电子
His success in his career was due to his determination __________ what seemed impossible.
A．of doing
B．with doing
C．doing
D．to do
BCR识别抗原的特点是（）。
A.受MHCⅠ类分子的限制性
B.受MHCⅡ类分子的限制性
C.识别抗原的线性决定簇
D.直接结合游离抗原
E.受MHC样分子的限制
