Three point charges +3mu C , +4mu C and +6mu C respectively are placed at three vertices of an equilateral triangle ABC of side a . The magnitude of the electric field at a point midway on side AB of equilateral triangle is
A) Directly proportional to a^2 b) Directly proportional to 1/a^2
C) Inversely proportional to a^3. D) Directly proportional to a
