[单选题]
Charge +2q is placed at the origin and charge:6(quy8 c8dy pvbwdz/)k uz: )mu)fqc -q is plp x1tms:m:n54pee n. eaced at x = 2a. Where can a third positive charge +q be placed so t x4:e5 mpe1n:e nsm.pthat the force on it is zero?
A. $3.4 \; a$
B. $6.8 \; a$
C. $8.6 \; a$
D. $9.3 \; a$
