Draw the condensed structural formula for $\mathbf{a}$ and $\mathbf{b}$ and the line-angle structural formula for $\mathbf{c}$ and $\mathbf{d}$.
a. 3-iodopentane
b. 3 -ethyl-2-methylpentane
c. 1,5 -dibromo-3-methylheptane
d. $1,1,5$ -trichloropentane