1. Correct the errors if necessary. 1. Since when are they waiting for us? 2. I have been looking for my passport since

1. Since when have they been waiting for us? 2. I have been looking for my passport since I came home. 3. His friends have had this building for ten years. 4. In recent years, scientists have developed many new machines.Пояснение: Предлоги for и since употребляются в большинстве случаев с временами Present Perfect и Present Perfect Continuous.