Which explanation for the corresponding R language is correct?

You can use subtractions on factors to determine the differences across levels

$R$ is case$-$sensitive$,$ so a variable with a name $"x"$ is larger than a variable with a

name $"$x$"$

$=$ and are the two ways to assign objects in $R.$ The difference is that $=$ will not

create objects if it is used to pass values to parameters in a function.

Inf is a value that stands for invalid numerics