watch-watched; are-were
take-took; did-do
visited-visit; said-say
stay-stayed; make-made
come-came; went-go
got-get; ate-eat
watch是觀看的意思,沒有cpmputed這個詞,應該是computed,它是compute的過去式,是計算的意思
只有謂語動詞watch變成過去式,而play是非謂語動詞形式,變成現在分詞playing或不帶to的不定式,即原形,這個句子變成過去式有兩種,即
He watched his dog playing with his cat.他看到他的狗和貓正在玩耍.(看到的是一個畫面,不是全過程.)
He watched his dog play with his cat.他看到他的狗和貓玩耍.(看到的是整個過程.)