Which of the following is correct?

Generate the following cyclopropanes in one step from any needed precursor:

$1,1-\mathrm{Dimethylcyclopropane}$

Generate the following cyclopropanes in one step from any needed precursor:

$1,2-\mathrm{Dimethylcyclopropane}$ (ignore cis-trans isomers).

Predict the predict of the reaction with $\mathrm{HBr}$ with (i) cyclopropane (ii) $1,1-$dimethylcyclpropane

Compare the rates of these reactions.

(b) Calculate the $∆{\mathrm{H}}_{\mathrm{c}}$ per ${\mathrm{CH}}_2$ unit for the first six cycloalkanes. The $∆{\mathrm{H}}_{\mathrm{c}}$ 's in $\mathrm{kJ}/\mathrm{mol}$ are: cyclopropane $-2090$; cyclobutane $-2718$; cyclopentane $-3288$, cyclohexane $-3918$, cycloheptane -4632, cycloocatne $-5304$.

How do the calculated values in (b) relate to the ring stability?