A Multiphase problem
 

Dear everyone, I am carrying on solid-liquid two phase simulation now. But i can not choose the solid particle as the secondary phase in the Basic Setting—>Fluid List, just only air and water for option. i did create a new solid material and the new solid material is visible in the
'Outline' tree view in CFX-Pre, under the 'Materials' object. i do not know why i can not choose it.

i appreciate anyone's kind help...