Final answer:
The text provided does not contain enough information to determine who Trevor's mother thinks left the "present" in the trash. Additional context from the story is needed to accurately answer the student's question.
Step-by-step explanation:
The question asks who Trevor's mother believes left the "present" in the trash. Unfortunately, the provided excerpts do not directly address Trevor or his mother, or a situation directly involving a present in the trash. To accurately answer the student's question, one would need the appropriate context from the source material, which appears to be a narrative work of fiction.
Without the specific details from the text that pertain to Trevor and his mother, it is impossible to provide a confident answer. Students are encouraged to review the story more closely to discover hints or explicit mentions that could shed light on who Trevor's mother suspects of leaving the present in the trash.