Final answer:
Option (d) best revises sentence 18, placing the fact of the child's disappearance before the narrator's emotional response, therefore increasing the anxiety tone.
Step-by-step explanation:
The best way to revise the syntax of sentence 18 to heighten the tone of increasing anxiety is option (d). We found that our three-year-old Amy was missing one day after we had traveled some distance. I still can't recall this without a sick feeling here in the pit of my stomach.
Option (d) best revises sentence 18, placing the fact of the child's disappearance before the narrator's emotional response, therefore increasing the anxiety tone.
This revision effectively builds suspense by first stating the alarming fact of the child's disappearance and follows it with the narrator's emotional reaction, enhancing the anxious tone of the situation.