This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oral Cavity, Subject name: Surgery
[{'content': 'The prognosis for squamous carcinoma of the floor of the mouth is adversely affected by which of the following?Composite resection specimen of a T4 floor of mouth squamous cell carcinoma \nSelect and explain. \nA. Poor differentiation of tumor, B. Nonverrucous carcinoma, C. Presence on left side, D. No tongue involvement', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Poorly differentiated squamous cell carcinoma of the floor of the mouth tends to be more invasive than better-differentiated tumors. Poorer prognosis can be expected when invasion is larger than 9 mm, perineural invasion is noted, and lymph node metastasis is evident.', 'role': 'assistant'}]