1、被动语态的结构：
主语+be动词的不同时态+过去分词（by）+（其它）
现在进行时态的被动语态：
主语+am/is/are+being+过去分词+（by）+（其它）
过去进行时态的被动语态：
主语+was/were+being+过去分词+（by）+（其它）
2、Now please pick out two more sentences in the passive voice using the present
continuous tense.
①I wait here because we are becoming endangered in Zimbabwe.
②Daisy turned around and saw she was being watched by an excited elephant.
3、单项选择（被动语态小结）
①A lot of tall buildings D in our city since 1997.
A have built B are being built C has been built D have been built
②Look, the new house B.
A is painting B is being painted C is painted D has painted
③Great changes A since 1998.
A have taken place B have been taken place C took place D take place
以下词汇不能使用被动语态：happen、take place、occur、come about