[单选题]
Two point charges each have a-1mj f9 /gru yw08jkyj1acn:t valuehvo u;;v /1)g2gubish of 3.0 C and are separated by a distance of 4.0 m. What is the electsbguvh oghi1u ) 2v;;/ric field at a point midway between the two charges?
A. zero
B. $9.0 \times 10^{7} \; N/C$
C. $18 \times 10^{7} \; N/C$
D. $4.5 \times 10^{7} \; N/C$
