有人能帮忙解决以下问题吗？
The following packages have unmet dependencies:
libmono-cil-dev : Depends: libmono-http4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-microsoft-web-infrastructure1.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-oracle4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-data-services4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-design4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-drawing4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-drawing-design4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-messaging4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-reactive-windows-forms2.2-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-runtime4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-servicemodel4.0a-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-servicemodel-activation4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-servicemodel-discovery4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-servicemodel-routing4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-servicemodel-web4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-serviceprocess4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-abstractions4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-dynamicdata4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-extensions4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-extensions-design4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-http-selfhost4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-http-webhost4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-mvc3.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-routing4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-services4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-webpages2.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-webpages-deployment2.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-web-webpages-razor2.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-windows-forms4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-windows-forms-datavisualization4.0a-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libmono-system-xml-serialization4.0-cil (= 5.18.1.0-0xamarin4+debian8b1) but it is not going to be installed
Depends: libnunit-cil-dev (>= 2.4) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.