Which sentence contains a misplaced modifier?

A misplaced modifier occurs when a descriptive phrase is positioned in a sentence in a way that suggests an incorrect or unintended meaning. In the chosen answer, the sentence "The investigator tested the participants who were using this procedure" implies that only the participants who were currently using the procedure were tested, which can create ambiguity about what the subject is doing.

In contrast, the other options present clearer meanings. The first sentence suggests that the procedure was used by the investigator during testing, without misdirecting the reader about who is using it. The third option indicates that the procedure was utilized in the process of testing participants, maintaining clarity. Therefore, option B stands out as having a misplaced modifier because it creates confusion around the relationship between the investigator and the usage of the procedure.