Step 1: Lethargus is the resting phase just before a nematode moults, not the moult itself.
Step 2: Rule out 'killing and fixing' as it is a lab technique, and 'desiccation' as it relates to water-loss survival, not moulting.
Step 3: What remains is an inactive, non-feeding state, i.e., quiescence.
Step 4: Correct answer: Quiescence.