Answer:
Option c - never
Step-by-step explanation:
Given : Two planes intersect in exactly one point.
Solution : Two planes never intersect in exactly one point.
Because, If two planes intersect, then their intersection is a line.
and a line consist of two points.
As shown in the figure attached.
There are two planes G and H and their intersection is a line l.
And the line l consist of two points.
Therefore, Option c is correct - Never
