Past Perfect Simple or Continuous

It was a relief to find the documents. I (look) (a)   for them all afternoon.

He was dismissed, even though, in his opinion, he (a)   (not/do) anything wrong.

It was not the first time I'd met him. We (meet) (a)   many times before.

He called me at eleven in the evening to tell me that he (a)   (find/finally) a solution.

When he (a)   (finish) his speech, he waited for the reaction of the audience. But no one said a word.

By the time I came back from my business trip, a lot of things (a)   (changed)

The doctor asked me how long I (a)   (have) the symptoms

It was more than a month before we realised what (a)   (happen) to him.

We (a)   (work/already) on this project for a month before we found a fundamental flaw.

The invoice (a)   (not/arrive/still) by the end of the week so we sent them a strong reminder.