单选题 The book you want is not ______ now. I will let you know as soon as it is returned to the library.

【正确答案】 C
【答案解析】[考点] 形容词
[解析] useful“有用的”;possible“可能的”;available“可用的,有效的,可买到的,可借到的”;practical“实际的,实用的”。