Write the following sets in roster form : F=The set of all letters in the word BETTER

Question

$\begin{array}{1 1}(A)\;F=\{B,E,T,R\}\\(B)\;F=\{B,T,R\}\\(C)\;F=\{T,R\}\\(D)\;F=\{B,E\}\end{array}$