Answer:
1. firm and stiff: not bending or easily moved into a different shape or position
lengths of rigid plastic pipes
2. inflexible: applied or carried out strictly, with no allowances or exceptions
a rigid set of rules
3. inflexibly adhered to: kept unchanged or strictly adhered to
rigid opinions
4. refusing to change: unwilling to change or adapt behavior, opinions, or attitudes
Despite arguments to the contrary, she remained rigid in her stand
it means that they are fluid-liquid
rigid-hard