The vector 'letters' is a built$-$in vector to $\text{'}R\text{'}$ and contains the lower case English alphabet.

a$.$ Extract the $9$ th element of the 'letters' vector.

b$.$ Extract the sub$-$vector that contains the $9$th$,11$th$,$ and $19$th elements.

c$.$ Extract the sub$-$vector that contains everything except the last two elements.