### Instruction:

Extract the cause and effect entities from the following sentence:
Because many, if not most, NAS systems are not new, but rather, evolutionary improvements of existing NAS systems, a top-down process is not always appropriate

### Assistant:

KEYWORD: Because many, if not most
VARIABLE: a top-down process
NEGATION: is not
CONDITION: always appropriate
AND: but rather
EFFECT_1: a top-down process is not always appropriate
CAUSE_1: NAS systems are not new
CAUSE_2: evolutionary improvements of existing NAS systems

