công thức thì QKĐ là : ( dạng động từ thường )
` -> ` ( + ) : S + v-ed / v2
` -> ` ( - ) S + didn't + V nguyên mẫu
` -> ` ( ? ) : did + S + V nguyên mẫu
công thức thì QKĐ : ( dạng tobe )
` -> ` ( + ) : S + was / were + ...
` -> ` ( - ) S + wasn't / weren't
` -> ` ( ? ): was / were + S + V nguyên mẫu