基本语法。 1. The streets here_____ (clean) b

问题：

基本语法。

1. The streets here _____ (clean) by the cleaners every morning.

2. These flowers _____ (water) once every three days.

3. Many new things _____ (invent) by the scientists in the 20th century.

4. Yesterday a composition on protecting animals _____ ( write) by the students of our class.

5. The little girl had learned to play the piano  _____ the age of five.