我在下面的代码中有一个引用有问题，它抱怨第三一个是：
Package inputenc Error: Keyboard character used is undefined
代码如下：
\documentclass[runningheads,a4paper]{llncs}
\usepackage{amssymb}
\setcounter{tocdepth}{2}
\usepackage{graphicx}
\usepackage[latin1]{inputenc}
\usepackage[english]{babel}
\usepackage{float}
\usepackage{booktabs}
\usepackage{mathtools}
\usepackage{amsmath}
\usepackage[english]{babel}
\usepackage{booktabs,array}
\usepackage{lipsum}
\usepackage{hhline}% http://ctan.org/pkg/hhline
\setcounter{secnumdepth}{5}
\begin{document}
\begin{thebibliography}{4}
\bibitem{jour} Othmane, Lotfi ben, Ranchal, Rohit, Fernando, Ruchith, Bhargava, Bharat, Bod-den, Eric. (2015). Incorporating attacker capabilities in risk estimation and mitigation. Comput. Secur., 51(C), 41-61. doi: 10.1016/j.cose.2015.03.001
\bibitem{book} Alberts C, Dorofee A. Managing Information Security Risks: The OCTAVE Approach, Addison-Wesley Professional.2002.
\bibitem{jour} Schneier, B.: Attack Trees. Dr. Dobb’s Journal (1999).
\bibitem{proceeding1} Czajkowski, K., Fitzgerald, S., Foster, I., Kesselman, C.: Grid
Information Services for Distributed Resource Sharing. In: 10th IEEE
International Symposium on High Performance Distributed Computing, pp.
181--184. IEEE Press, New York (2001)
\bibitem{proceeding2} Foster, I., Kesselman, C., Nick, J., Tuecke, S.: The Physiology of the
Grid: an Open Grid Services Architecture for Distributed Systems
Integration. Technical report, Global Grid Forum (2002)
\bibitem{url} National Center for Biotechnology Information, \url{http://www.ncbi.nlm.nih.gov}
\end{thebibliography}
\end{document}