英文高手請進

請說出下列字句分別：

1)to be decreased 等待/將會被減
There are too many seats in the classroom, and the number of seats is to be decreased.

2)is being decreased 現在正不斷被減 (進行中, i.e. 未完)
The number of seats in the classroom is being decreased.

3)was being decreased 錯!!!! 沒有這寫法的

4)had been decreased 在某事發生之前己經被減
e.g. The number of seats in the classroom had been decreased before the students walked in.

5)has been decreased 現在已經被減
e.g. The number of seats in a classroom has been decreased by 10.

6)had been decreasing
唔知道有冇這種寫法. 未見過.

7)has been decreasing 一直以來都被減去/ 下降
e.g. The number of seats in the classroom has been decreasing since last year.