A line or edge.
Yes, of course it is.
Yes, it is possible for three distinct planes to intersect at a line.
A trapezium (trapezoid).
Either 0 or 1 plane(s).
The intersection of two distinct planes is a line. The set of common points in the line lies in both planes.
A line
Two distinct planes will intersect in one straight line.
A line or edge.
The leg of a trapezoid is one of the two nonparallel sides of the trapezoid. However, the base of a trapezoid is of the two parallel sides of the trapezoid.
If two distinct planes intersect, therefore their intersection is a line.
Yes, of course it is.
Yes, it is possible for three distinct planes to intersect at a line.
No.
a point
A trapezium (trapezoid).
Either 0 or 1 plane(s).