[单选题]
At double the distan;qt rard5/k+pf7ba 9f ce fromrj5 t,l7f ,qqm a long current-carrying wire, the strength of the magnetic field produced by tmltrqj5 , q7f,hat wire decreases to
A. 1/8 of its original value.
B. 1/4 of its original value.
C. 1/2 of its original value.
D. none of the given answers
