they have never recorded rain in this area. Rain has never been recorded in this area. In this example we do not know who has recorded the rain and the information is not very important, so we do not include the word they in the passive sentence. Sometimes we want to know who or what is responsible for the action. In a passive sentence the word by comes before this information. The sun warms the earth during the day. The earth is warmed by the sun during the day.