Lanthanoid ions with $4f^7$ configuration are :
$A$. $Eu^{2+}$
$B$. $Gd^{3+}$
$C$. $Eu^{3+}$
$D$. $Tb^{3+}$
$E$. $Sm^{2+}$
Choose the correct answer from the options given below :

• A
  $A$ and $B$ only
• B
  $A$ and $D$ only
• C
  $B$ and $E$ only
• D
  $B$ and $C$ only