estuvieron desmantelando
-they/you were dismantling
Pretérito progresivo para el sujetoellos/ellas/ustedesdel verbodesmantelar.

desmantelar

Trabajaban quieta, invisible y engañosamente; durante todo el tiempo que estuvieron desmantelando el gobierno del Imperio Romano secretamente, proclamaban públicamente su lealtad y apoyo al imperio.
They worked quietly, invisibly and deceitfully; during the entire time they were secretly dismantling the government of the Roman Empire, they publicly proclaimed their unswerving support of it.
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