Which of the following signs and symptoms is classic for a patient with rheumatoid arthritis

A．Joint swelling, joint stiffness in the morning, and bilateral joint involvement.

B．Crepitus, development of Heberden's nodes, and anemia.

C．Pain on weight-bearing, rash, and low-grade fever.

D．Fatigue, leukopenia, and joint pain.

直流电机中，定子主要由机座、主磁极、（）和电刷装置组成。

A、转轴

B、换向极

C、换向器

D、电枢绕组