[单选题]
What is the magnetic field at ther owh-ff nd;wn,( uc 54qzmfcdv)z;s(4j* pp( cei, d8dx;o6ylonter of a circular loop of wire of radius 4.0 cod yl;i 8dx6o,m when a current of 2.0 A flows in the wire?
A. $1.3 \times 10^{-6} \; T$
B. $3.1 \times 10^{-6} \; T$
C. $1.3 \times 10^{-5} \; T$
D. $3.1 \times 10^{-5} \; T$
