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Let $S$ be the set of points in space whose rectangular coordinates are the same as their cylindrical coordinates, in the same order.

Which of the following statements is TRUE?

The set $S$ is empty.

The set $S$ consists of one point.

The set $S$ consists of a plane.

The set $S$ consists of a line crossing the origin.

The set $S$ consists of a line that is parallel to one of the coordinate axes.