In a mechanism, the fixed instantaneous centres are those centres which
(a) remain in the same place for all configurations of the mechanism
(b) vary with the configuration of the mechanism
(c) moves as the mechanism moves, but joints are of permanent nature
(d) none of the mentioned
I have been asked this question in an online quiz.
My doubt is from Number of Degrees of Freedom for Plane Mechanisms topic in division Simple Mechanisms of Machine Kinematics