Past Perfect Continuous

Past Perfect Continuous
The Past Perfect Continuous is used for a continuous action that was completed at some point in the past.
It is formed by the past perfect of the verb “to be” (had been) and the base of the main verb +ing.
In the negative form use the past of the verb “to have” (had) + not been + the base of the main verb + (-ing)
In the interrogative form use the past of the verb “to have” (had) + subject + past participle of the verb “to be” (been) + the base of the main verb + (-ing)