[单选题]
Charge +2q is placed at the origin and charge -2jln.hn5 t/ia) (/f6qbljecz, ( utxkq is placed at x = 2a. byf:2)z/9yu1hf u tojWhere can a third positive charge +q be placed so that the ftfyh/z2 u:uo9yfb1j )orce on it is zero?
A. $3.4 \; a$
B. $6.8 \; a$
C. $8.6 \; a$
D. $9.3 \; a$