Comparing between SN2 and E2 Question
I am confused between the questions B. And C. The earlier is SN2 and later is E2. But what makes the difference?
The most important factor in these reactions are nucleophiles. Here, the use of strong base (Sodium methoxide) in both of the reactions favors the bi-molecular mechanisms ($\ce{S_N2}$ and $\ce{E2}$). 

Now, the second factor would be degree of halogen-linked carbon. Lower degree carbons ($\ce{\text{deg.} &lt; 2}$) favor $\ce{S_N2}$, while higher degree favors $\ce{E2, E1, S_N1}$. So, $\ce{S_N2}$ is favored in first and $\ce{E2}$ in second. 

Temperature conditions and nature of solvent are least important factors, and should be looked up when above two factors are similar.