Was he cooking at six last night?为什么cook要加ing

Was he cooking at six last night?为什么cook要加ing What were you doing at 7:30 last night? 请问do为什么加ing 连词成句:I,was,eight,at,dinner,last,cooking,night He asked me what happened at 8:00 last night 为什么不用was happen grandma is good at ------(cook).she -----(cook)last night 用词 he was listening to the radio at nine last night he was at the party last night改否定句 Where was your brother at this same time last night?He was w Mr Green,night,the school,at six,left,last I was expecting him here at five forty-five.为什么expect要加ing I was at home last night.(否定) 请问I free myself from cooking.为什么cook用ing形式?