Using Newman projections, draw each of the following molecules in its most stable conformation with respect to

Question:

Using Newman projections, draw each of the following molecules in its most stable conformation with respect to the bond indicated:
(a) 2-methylbutane, C2-C3 bond;
(b) 2,2-dimethylbutane, C2-C3 bond;
(c) 2,2-dimethylpentane, C3-C4 bond;
(d) 2,2,4-trimethylpentane, C3-C4 bond.