无法在 ubuntu 20.04 中安装 g++

问：

我在这个网站上看到了一些类似的问题。
但是他们都没有得到答复，我无法在那里发表评论，因为我的声望点数较少。

当我运行时，我收到以下错误：sudo apt install g++

Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 g++ : Depends: gcc (= 4:9.3.0-1ubuntu2) but it is not going to be installed
       Depends: g++-9 (>= 9.3.0-3~) but it is not going to be installed
       Depends: gcc-9 (>= 9.3.0-3~) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

当我运行时，我收到以下错误：sudo apt install build-essential

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 build-essential : Depends: gcc (>= 4:9.2) but it is not going to be installed
                   Depends: g++ (>= 4:9.2) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

我需要在 ubuntu20.04 中安装 g++。

感谢您的帮助！