Answer: C) Past perfect continuous tense.
Explanation for this question is being written.
Answer: C) Had been walking.
Answer: B) 'd already been working.
Answer: B) Had been walking.
Answer: A) Had been waiting.
Answer: C) Had been running.
Answer: C) How long had you been studying English in US?
Answer: B) Had been waiting.
Answer: C) Had been sitting.
Answer: A) Had been learning.
Answer: D) Past perfect continuous tense.
Answer: A) True
Answer: B) Had been listening.
Answer: C) Had never been.
Answer: B) To talk about longer continuous actions or situations that started before the main events happened and have continued up to that point.
Answer: D) Past Perfect Continuous.
Answer: B) B
Answer: B) Had been traveling.
Answer: B) Had been living.
Answer: C) Had been.
Answer: B) He was tired because he had been working all night.
Answer: D) Past perfect continuous.
Answer: C) Had been studying.
Answer: D) Had been practicing.
Answer: D) Had been waiting.
Answer: C) Had been driving.
Answer: A) Correct
Answer: A) I had been knowing my best friend since kindergarten.
Answer: C) She'd been working.
Answer: E) Past Perfect Continuous.
Answer: C) Had been working.
Answer: D) Had been blocking.
Answer: D) Been quarreling.
Answer: C) C
Answer: B) I had been waiting for thirty minutes when my friend finally showed up.
Answer: A) Past Perfect Continuous.
Answer: A) She had been listening to music.
Answer: B) Had been gardening.
Answer: C) Had already been waiting.
Answer: D) They had been studying for hours before the exam started.
Answer: C) Had been reading.
Answer: B) She had been studying when I called her.
Answer: A) Past perfect continuous tense.
Answer: C) Had been raining.
Answer: D) Had been typing.
Answer: A) Had/been cleaning.
Answer: B) Past perfect continuous tense.
Answer: B) Incorrect
Answer: A) Had been working.
Answer: A) Had been cooked.