句型转换：1、Thousands of tourists visit the West Lake every year .(改为被动语态）
2、The language lab should always be kept clean .(改为一般疑问句）
3、We weren't allowed to enter the theater by the guard .(改为主动语态）
4、The pie plate was invented ( by accident ) （对括号内部分提问）
5、The foreign teachers are often invited to dinners ( on the weekends ).(就画线部分提问）