Identify $A, B, C, D, E, R$ and $R^1$ in the following reactions:
$Cyclohexyl-Br + Mg$ $\xrightarrow{dry\,ether} A$ $\xrightarrow{H_2O} B$
$R-Br + Mg$ $\xrightarrow{dry\,ether} C$ $\xrightarrow{D_2O} CH_3-CH(D)-CH_3$
$CH_3-C(CH_3)_2-C(CH_3)_2-CH_3 \xleftarrow{Na/ether} R^1-X$ $\xrightarrow{Mg} D$ $\xrightarrow{H_2O} E$

(B) $1.$ $Cyclohexyl-Br + Mg$ $\xrightarrow{dry\,ether} Cyclohexyl-MgBr (A)$ $\xrightarrow{H_2O} Cyclohexane (B)$
$2.$ $CH_3-CH(Br)-CH_3 (R) + Mg$ $\xrightarrow{dry\,ether} CH_3-CH(MgBr)-CH_3 (C)$ $\xrightarrow{D_2O} CH_3-CH(D)-CH_3$
$3.$ $2(CH_3)_3C-X (R^1-X) \xrightarrow{Na/ether} (CH_3)_3C-C(CH_3)_3$ (Wurtz reaction)
$4.$ $(CH_3)_3C-X$ $\xrightarrow{Mg} (CH_3)_3C-MgX (D)$ $\xrightarrow{H_2O} (CH_3)_3CH (E)$
Thus:
$A = Cyclohexylmagnesium\,bromide$
$B = Cyclohexane$
$C = CH_3-CH(MgBr)-CH_3$
$D = (CH_3)_3C-MgX$
$E = (CH_3)_3CH$
$R = CH_3-CH(Br)-CH_3$
$R^1 = (CH_3)_3C-$