Simplify the following text for a Grade 9 native English-speaking person.
Original: All lanthanoids are f-block elements , corresponding to the filling of the 4f electron shell , except for lutetium which is a d-block lanthanoid .
Simplified: All lanthanides are f-block elements , corresponding to the filling of the 4f electron shell . Lutetium , which is a d-block element , is also generally considered to be a lanthanide .