While he( write)..... a letter ,the telephone( ring)........ as he(go)......... to answer it ,he(hear).......... knock on the door.Telephone(still,ring)....... while he( walk)......... to the door, but just as he (open) .........it it (stop)............... Giải thích tại sao làm vậy

While I (write) _____was writing_____ a letter, the telephone (ring) _______rang___; as
he (go) _____went_____ to answer it, he (hear) _____heard_____ a knock on the door;
the telephone (still, ring) ______had still rung____ while he (walk) ____was walking______ to the door, but
just as he (open) _____opened_____ it, it (stop) ___stopped_______.

đây là thì QKTD và thì QKĐ

công thức thì QKTD :

+ S + was/were + V-ing (+ O)

- S + was/were + not + V-ing (+ O)

? was/were + S + V-ing (+ O)?

công thức thì QKĐ

TOBE :

+ S + was/ were +

- S + wasn't / weren't + 

? was / were + S + ...

ĐT thường

+  S + V-ed +…

-  S + did not + V

? : Did + S + V