Two identical charges `+Q` are kept fixed some distance apart.A small particles `P` with charge `q` is placed midway between them . If `P` is given a small displacement `Delta` ,it will undergo simple harmonic motion if
(i) `q` is positive and `Delta` is along the line joining the charges
(ii) `q` is positive and `Delta` is perpendicular to the line joining the charges
(iii) `q` is negative and `Delta` is perpendicular to the line joining the charges
(iv) `q` is positive and `Delta` is along the line joining the charges
A. `(i) ,(ii)`
B. `(i),(iii)`
C. `(ii),(iii)`
D. `(i),(iv)`
