[单选题]
Two point charges of +3.0 mC and -7.0 m/u (o- lbx.+l(2 ymsyut jrpk6p/,rg cC are plw-/(jyzul- tmaced at x = 0 and x = 0.20 m. What is the magnitude of the electric field at the point midwlm ytu-- wjz(/ay between them?
A. $1.8 \times 10^{6} \; N/C$
B. $3.6 \times 10^{6} \; N/C$
C. $4.5 \times 10^{6} \; N/C$
D. $9.0 \times 10^{6} \; N/C$
