Why was she speaking ...
When was Sam risiting...
With whom was she going...
To whom was David writing...
When were they playing...
For whom was Helen buying...
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I have received the enquiry from Green & Co  (this week.just, this morning ) эти три варианта pr. Perfect I have just received the enquiry from Green & Co
I received the enquiry from Green and Co (yesterday, two days ago, last month) эти три варианта past simple 

We visited some places of interest yesterday, a week ago. 
We have visited some places of interest today,
We have already visited some places of interest
 
They were in the office yesterday
they have been in the office lately, this week, 
they have just been in the office

1. What are you doing? - We are preparing for the concert.
2. Where are you going? - I'm going to the library.
3. Where is Nicholas? - He's in the reading room. Is doing his homework there. Nicholas often does his homework  in the reading room.
4. Is Lena at home? - No, it's not at home. She is having a music lesson. She always has music classes at this time.
5. Do not make noise. Kovalenko is speaking on the telephone.
6. Do not go into that room. There's a group of our students sitting a Maths exam.
7. Students sit examinations twice a year.
8. His son is going to become an economist.