What feature distinguishes the subjects in the 'stretto' section of a fugue?

In the context of a fugue, the 'stretto' section is characterized by the overlapping of subjects, which creates a sense of increased intensity and urgency within the musical texture. During this section, the main theme, or subject, is introduced in quick succession by different voices. This overlapping occurs in such a way that one voice enters with the subject while another voice is still presenting the preceding statement of the same theme. This close juxtaposition of the subjects heightens the dramatic effect and showcases the counterpoint characteristic of fugal writing.

The other choices do not accurately capture the defining feature of a stretto section. Spacing subjects apart, restating them in different keys, or utilizing different themes does not align with the fundamental concept of stretto, which is essentially about the immediate and close presentation of the same musical idea. Hence, the overlapping nature of subjects in the stretto section is what distinctly defines this moment within a fugue.