11. Somebody (knock) on the front door as I (have) breakfast.

{"english_answer"=>"Somebody knocked on the front door as I was having breakfast.", "explanation"=>"This sentence describes a past action that interrupted another ongoing past action. 'Knock' becomes the simple past tense 'knocked', and 'have' becomes the past continuous tense 'was having' because it was in progress when the knocking happened."}