ABCD is bar mechanism, in which AD is the fixed link, and link BC, is in the form of a circular disc with centre P. in which one of the following cases P will be the instantaneous centre of the disc?
(a) If it lies on the perpendicular bisector of link BC
(b) If it lies on the intersection of the perpendicular bisectors of BC & AD
(c) If it lies on the intersection of the perpendicular bisectors of AB & CD
(d) If it lies on the intersection of the extensions of AB and CD