The reaction conditions leading to the best yield of $C_2H_5Cl$ are:

• A
  $C_2H_6 \, (\text{excess}) + Cl_2 \, (\text{excess}) \xrightarrow{\Delta }$
• B
  $C_2H_6 \, (\text{less}) + Cl_2 \, (\text{less}) \xrightarrow{\Delta }$
• C
  $C_2H_6 \, (\text{excess}) + Cl_2 \, (\text{less}) \xrightarrow{\Delta }$
• D
  $C_2H_6 \, (\text{less}) + Cl_2 \, (\text{excess}) \xrightarrow{\Delta }$