Which expression below evaluates to true if and only if variable $ch$ of char type is a lowercase letter or an uppercase letter?

a$.($ch a$\text{'}|$ ch $>=\text{'}$z$\text{'})$ && $($ch A$\text{'}|$ ch $>=\text{'}$Z$\text{'})$

b$.($ch ${?}^{\text{'}}{a}^{\text{'}}$&& ch $\text{'}$z$\text{'})$ ch $\text{'}$Z$\text{'})$

C$.($ch $\text{'}$a$\text{'}||$ ch $\text{'}z\text{'})||($ch $\text{'}\text{'}$A$\text{'}||$ ch $\text{'}$ Z$\text{'})$

d$.($ch $\text{'}$a$\text{'}$ && ch $\text{'}$z$\text{'})$ & & $($ch ${?}^{\text{'}}{A}^{\text{'}}$&& ch $\text{'}$Z$\text{'})$