In the given pairs of reactions,in which pair is the second reaction more reactive than the first toward $S_{N}2$ reaction?

• A
  $CH_{3}CH_{2}Cl + CH_{3}CH_{2}O^{-} \to CH_{3}CH_{2}OCH_{2}CH_{3}$ (or) $CH_{3}CH_{2}Cl + CH_{3}CH_{2}OH \to CH_{3}CH_{2}OCH_{2}CH_{3}$
• B
  $CH_{3}CH_{2}Cl + EtO^{-} \to CH_{3}CH_{2}OEt$ (or) $CH_{3}CH_{2}Cl + EtS^{-} \to CH_{3}CH_{2}SEt$
• C
  $EtCl (1 \ M) + CH_{3}O^{-} (2 \ M) \to EtOCH_{3}$ (or) $EtCl (2 \ M) + CH_{3}O^{-} (1 \ M) \to EtOCH_{3}$
• D
  $EtBr + Ph_{3}P \to EtP^{+}Ph_{3}$ (or) $EtBr + Ph_{3}N \to EtN^{+}Ph_{3}$