What sequence of steps represents the best synthesis of $4-heptanol$ $(CH_3CH_2CH_2)_2CHOH$?

• A
  $CH_3CH_2CH_2MgBr$ $(2 \ moles)$ $+$ formaldehyde $(H_2C=O)$ in diethyl ether followed by $H_3O^{+}$
• B
  $CH_3CH_2CH_2MgBr$ $+$ butanal $(CH_3CH_2CH_2CH=O)$ in diethyl ether followed by $H_3O^{+}$
• C
  $CH_3CH_2CH_2CH_2MgBr$ $+$ acetone $[(CH_3)_2C=O]$ in diethyl ether followed by $H_3O^{+}$
• D
  $(CH_3CH_2CH_2)_2CHMgBr$ $+$ formaldehyde $(H_2C=O)$ in diethyl ether followed by $H_3O^{+}$