[单选题]
The potential difference beta dg 5id4tg,dk :6((7ybh joahween the terminals of a u-rv,c .h8;pdhj)+skli j n rvb+l/u+battery, when no current flows to an external circuit, is referred to as therd;cr8j, +p/hkjh +u+sn- vl.lbuv i)
A. battery emf
B. terminal voltage
C. battery power
D. battery rating
