单选题 It is not ＿＿＿＿＿＿＿ for me to return all the books to the library now because I still need some of them for my research. 的答案

成人教育远程网络教育函授网上考试【专科英语I】课程在线考试模拟试题正确答案解析，免费查看【专科英语I】作业答案。
题目内容：
It is not ＿＿＿＿＿＿＿ for me to return all the books to the library now because I still need some of them for my research.
题目选项
continuous
difficult
convenient
sufficient

参考答案价值：100%