Unlike with words, the presence of a particular CSF in a sentence is not trivially recognizable.
there are three versions of the TSD task: (1) we are given the sentence, a marked subset of its words comprising a CSF, and the ASF that has generated these words; (2) we are given the sentence and a marked subset of its words comprising a CSF, without knowing the generating ASF; (3) we are given only the sentence and we need to find the contained CSFs and their ASFs.