It's my new PC with a new os of ubuntu.
every time when I want to install software or update apt-get, this error will appear:
First, as the most usual functions the website given:
to type these commands:
sudo rm /var/lib/apt/lists/* -vf
sudo apt-get clean
sudo apt-get update
sudo apt-get upgrade
But not worked.
Finally, I reset the system settings:
See,"download from xx."
fix it from US's to this.
then it worked.