Every morning the pupils read the texts ____ in the classroom.

A．on the top of their voices

B．on the top of their voice

C．at the top of their voices

D．at the top of their voice

前列腺患者行直流电庆大霉素药物保留灌肠导入，骶部，腹部对置法，骶部电极接____极，下腹部电极接____极。