[1] [受動態] ※[2][3]ができるのに、[1]ができない??
(1) Hamlet [was written] by Shakespeare.
(2) English [isn't spoken] in this country. ※by them:省略
(3) The store [has] just [been closed](現在完了形・受動態).
(4) A doghouse [is being made](現在進行形・受動態) by my father.
(5) A lot of stars [can be seen](助動詞+動詞の受動態) in the sky. ※by us:省略
[2]
(1) 〇
(2) 〇
(3) The bathroom [was (being) (used)] at that time. ※過去進行形・受動態
(4) 〇
(5) This problem [has (been) (discussed)] over five years. ※現在完了形・受動態
[3]
(1) 〇
(2) 〇
(3) 〇
(4) 〇
参考にしてください。