so it requires
.net common language runtime to execute.main point is
when an application written in c# executes,the
common language runtime managing memory,performing
garbage collection,managing exceptions,providing many
services that you as a developer no need to write
code for.

the CLR understands intermediate language(IL) which
produced by c# compiler instead of producing machine
language.seeing the IL,CLR Just in time(JIT) compiles
it into compiled machine code within memory and then
executes it as mentioned before.

so because c# requires CLR,you have to have CLR installed
in the system.major operating systems come with the
CLR version and also it is available by windows update.
CLR is part of the .Net so when you see updates for
runtime of .Net framework,it must contains the FCL(
.Net framework class library) and the CLR.