Past Perfect Continuous Tense

Maria _________ (learn) English for two years before I ________ (move) to the United States.

Kevin __________ (study) English on his own for months before he ____ (enroll) in a language school.

They _________ (practice) English conversation with a native speaker every week for six months.

When I ______ (start) using that computer, my sister _________ (work) on it for hours.

I _________ (walk) for 20 minutes when I _______ (see) a squirrel.

They ____________ (swim) for fifteen minutes when the shark _________ (come).

Peter _____________ (not have) dinner when I ________ (arrive).

They __________ (not travel) before they ________ (decide) to stay home.

I _____________ (prepare) the presentation before the meeting _______ (start).

We ________ (plan) our vacation for months when we ________ (have) to cancel it at the last minute.