单选题 The manager gave her his ______ that the complaint would be investigated.
A. admission B. allowance C. assurance D. insurance

【正确答案】 C
【答案解析】[解析] A项的admission意为“允许进入”；B项的allowance意为“允许”；C项的assurance表示“保证”；D项的insurance表示“保险”。比较词义，C项适合，为正确答案。