[单选题]
Charge +2q is placed at the origin and charge -q is placed atb3iux:5uv 0,g:jqu aqc- e z:-o 8cymx x = 206gy a bqx-lrr4de ci+2c6c.ra. Where can a tx42c+yldr i rc.6eaq-6gcbr 0 hird positive charge +q be placed so that the force on it is zero?
A. $3.4 \; a$
B. $6.8 \; a$
C. $8.6 \; a$
D. $9.3 \; a$
