The directivity pattern resulting from the action of parasitic elements depends on 3 factors. These are:

a) (1) the tuning, determined by the length of the parasitic element, (2) the spacing between the parasitic and driven elements, (3) the diameter of the driven element
b) (1) the tuning, determined by the length of the parasitic element, (2) the spacing between the parasitic and driven elements, (3) the diameter of the parasitic element
c) (1) the tuning, determined by the length of the driven element, (2) the spacing between the parasitic and driven elements, (3) the diameter of the driven element
d) (1) the tuning, determined by the length of the driven element, (2) the spacing between the parasitic and driven elements, (3) the diameter of the parasitic element