candidates of some package are not available

[Aryan Choudhary]

E: Package 'libreadline6-dev' has no installation candidate
E: Package 'zlib1g-dev' has no installation candidate
E: Package 'libssl-dev' has no installation candidate
E: Package 'libyaml-dev' has no installation candidate
E: Package 'libsqlite3-dev' has no installation candidate
E: Package 'sqlite3' has no installation candidate
E: Package 'libxml2-dev' has no installation candidate
E: Package 'libxslt1-dev' has no installation candidate
E: Package 'libncurses5-dev' has no installation candidate
E: Package 'bison' has no installation candidate

[bitsnpcs]

Hello Aryan Choudhary,
have you tried changing the sources for updates ?