Viết lại câu: Keeping the environment clean is very important

1.Keeping the environment clean is very important.
-It's..........................................................................
2.They will show the time machine to the public when they finish it.
-the time machine........................................................................
3.He was delighted to receive his aunt's letter.
-He was delighted that...................................................................
4.Old car tires are recycled to make shoes and sandals.
-People........................................................................
5.I'm very sad that i wasn't accepted in that group.
-I'm very sad not ............................................
6.It's three years since I last spoke her.
-I haven't.............................................
7.Tam doesn't type as fast as she used to.
-Tam used.................................................
8.''Please turn down the radio for me'',said my father
-My father asked.......................................................
9.Lan will be fifteen next week.
-It is Lan's......................................
10.How long is it since you used the pen?
-When...................................................................