The lengths of the links of a 4-bar linkage with revolute pairs only are $$p,q,r$$ and $$s$$ units. Given that $$p < q < r < s.$$ Which of these links should be the fixed one, for obtaining a ‘double crank’ mechanism?

For the planar mechanism shown in Fig. select the most appropriate choice for the motion of link 2 when link 4 is moved upwards.