当我尝试使用
sudo apt-get update
它给出了这个错误：
Fetched 5.530 kB in 53s (104 kB/s)
W: GPG error: http://extras.ubuntu.com precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release Unable to find expected entry 'main/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)
E: Some index files failed to download. They have been ignored, or old ones used instead.
当我尝试访问 etc/apt 文件夹时，它说没有这样的文件或目录。
我怎样才能解决这个问题？