单选题 Don't forget to ______ your letter before you mail it.
A. fasten B. shut C. seal D. stick

【正确答案】 C
【答案解析】[解析] seal a letter“把信封上”。fasten“扎牢”；shut“关(窗、门等)”；stick“粘贴”stick a stamp to the letter“在信封上贴邮票”。