Identify the Swarts reaction from the following:

• A
  $R-CH_2-Br + NaI \xrightarrow[\text{acetone}]{\text{dry}} R-CH_2-I + NaBr$
• B
  $2 R-CH_2-Br + 2 Na \xrightarrow[\text{ether}]{\text{dry}} R-(CH_2)_2-R + 2 NaBr$
• C
  $2 C_6H_5Cl + 2 Na \xrightarrow[\text{ether}]{\text{dry}} C_6H_5-C_6H_5 + 2 NaCl$
• D
  $2 R-CH_2-Br + CoF_2 \longrightarrow 2 R-CH_2-F + CoBr_2$