[单选题]
A 15.0-mW laser puts out a narrow beam 2.00 mm in diameter. What is the ,m5w hjml2aq; *a(-bx-la ;pl f;xmfwave(e1 mnke bgmxd 5v*(8arage (rmegmn5 8m k vbex(1(a*ds) value of the magnetic field?
A. $4.5 \; mT$
B. $6.4 \; mT$
C. $9.0 \; mT$
D. none of the given answers
