Answer:
1) I will send the email today.
2) The employees must have left the documents behind.
3) (this is already written in active voice).
4) Have they read the instructions yet.
5) (this is already written in active voice).
6) They had to call the ambulance.
7) The mechanic will repair my car by next week.
8) At this moment, they are breaking down the old bridge.
9) (this is already written in active voice)
10) You need to leave the windows open.
11) My parents advised me to get a visa.
12) Why did you break the glass?
Step-by-step explanation:
Active voice = subject + verb + object
Passive voice = object+ verb + subject
Hope this helps! :)