### Instruction:

Extract the cause and effect entities from the following sentence:
Damage to COPVs can be difficult to detect because reliable NDE methods have not been developed

### Assistant:

VARIABLE: reliable NDE methods
CONDITION: been developed
KEYWORD: because
NEGATION: have not
CAUSE_1: reliable NDE methods have not been developed
EFFECT_1: Damage to COPVs can be difficult to detect

