什么是进行时的被动语态?

1.现在进行时的被动语态形式为：主语＋am，is，are＋being＋过去分词＋by＋宾语。
中文：她正在浇花。
(主)She is watering the flowers.
(被)The flowers are being watered by her.
2.过去进行时的被动语态形式为：主语＋was，were＋being＋过去分词＋by＋宾语。【参见BE】
中文：铃响时他们正在读书。
(主)They were reading books when the bell rang.
(被)Books were being read by them when the bell rang.