The punctuation marks are not used grammatically, but to indicate intonation. The period indicates a falling, or final, intonation contour, not necessarily the end of a sentence. Similarly, a question mark indicates rising intonation, not necessarily a question, and a comma indicates "continuing" intonation, not necessarily a clause boundary. In some transcript fragments in your readings you may see a combined question mark and comma, which indicates a rise stronger than a comma but weaker than a question mark. Because this symbol cannot be produced by the computer, the inverted question mark is used for this purpose.

."final" intonation:

? rising intonation:

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