Use of 'Since' and 'For'

How to use 'Since' in Perfect & Perfect Continues Tense 1. When Time is specified, or 'time' has its particular name, such as Morning, Evening, Noon, Monday, March, 2020, 1980 etc. For Example: He has been studying since morning . He has not seen her since Monday. She had been studying Geography since January . I have not seen him since last night. 2. When Past Indefinite is mentioned, such as He has been in hospital since he met an accident . He has not touched any book since he left the school. 3. ' for ' is used for a period of time For example: He has been studying books for two hours. They have been waiting for me for three weeks. They have been playing with toys for hours. I knew him for ten years. 4. ' ago' is used with past Indefinite Tense. For example: He went to Dubai two days ago They met me last night . They took our lunch an hour ago . He died two years ago . 1. I have been watching a movie ___ an hour. A) since B) ...