图示结构为（ ）体系。 A、几何不变无多余约束 B、几何不变有多余约束 C、瞬变 D、常变……

单项选择题Regarding to the polarization, which statement as follows is wrong? A、The polarization is used to indicate the degree of polarization of dielectric. B、If is the vector sum of dipole moments in a volume , we can obtain . C、The unit of polarization is . D、The polarization is the dipole moment per unit volume.

问答题指浅屈肌四条肌腱同时收缩时可（），单个收缩时可（ 或 ）