Я не могу установить программное обеспечение, которое я хочу!

Пожалуйста, помогите, я не могу установить программное обеспечение. Если я пытаюсь установить Google Chrome, это то, что я получаю

sthabiso@sthabiso-R519-R719:~$ sudo apt-get install libcurl3 libnspr4-0d libxss1[sudo] password for sthabiso: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package libxss1 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package libnspr4-0d is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  libnspr4

E: Package 'libnspr4-0d' has no installation candidate
E: Package 'libxss1' has no installation candidate

sthabiso@sthabiso-R519-R719:~$ 

Если я устанавливаю Light Spark, я получаю следующее

sthabiso@sthabiso-R519-R719:~$ sudo apt-get install lightspark browser-plugin-lightspark
[sudo] password for sthabiso: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package browser-plugin-lightspark is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package lightspark is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'lightspark' has no installation candidate
E: Package 'browser-plugin-lightspark' has no installation candidate

Если я устанавливаю Gnash

sthabiso@sthabiso-R519-R719:~$ sudo apt-get install gnash mozilla-plugin-gnash
[sudo] password for sthabiso: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package gnash is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package mozilla-plugin-gnash is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'gnash' has no installation candidate
E: Package 'mozilla-plugin-gnash' has no installation candidate

Я ничего не могу сделать, пожалуйста, помогите мне.