3. Choose the correct form of the verb for each sentence: 1) Many people believe that our climate has changed / has been changing very markedly. 2) I have collected / have been collecting the pictures with bridges since I graduated from university. Now I have collected / have been collecting enough to organize an interesting exhibition. 3) She has read / has been reading a fairy tale to the children since breakfast. They haven't finished / haven't been finishing yet. 4) Those people have waited / have been waiting for a tram for the last fifteen minutes. I'm afraid they don't know that the electricity has gone / has been going out. 5) What has happened / has been happening to Mary? John has rung / has been ringing her up the whole evening and nobody has answered / has been answering. 6) “You have come / have been coming out at last,” he said. “Well, I have stood / have been standing here long, and have listened / have been listening to the nightingale.” 7) So you have arrived / have been arriving. We have just spoken / have just been speaking of you. 8) “How long have you known / have you been knowing about it?” — “I have known / have been knowing it all the time.” 9) “Why have you turned / have you been turning off the music?” — “I have played / have been playing the CDs for hours; I'm tired now.”

1. Many people believe that our climate has been changing very markedly.
2. I have been collecting the pictures with bridges since I graduated from university. Now I have collected enough to organize an interesting exhibition.
3. She has been reading a fairy tale to the children since breakfast. They haven't finished yet.
4. Those people have been waiting for a tram for the last fifteen minutes. I'm afraid they don't know that the electricity has gone out.
5. What has happened to Mary? John has been ringing her up the whole evening and nobody has answered.
6. “You have come out at last,” he said. “Well, I have been standing here long, and have been listening to the nightingale.”
7. So you have arrived. We have just been speaking of you.
8. “How long have you known about it?” — “I have known it all the time.”
9. “Why have you turned off the music?” — “I have been playing the CDs for hours; I'm tired now.”

The present perfect continuous emphasizes an ongoing or recently continuous activity; the present perfect emphasizes a completed action, result, state, or event.