a) She could leave the box to the center of the room
->The box could be left to the center of the room.

b) Men found the light a long time ago
-> The light was found by men a long time ago.

c) Mr.Lam has been carried this bag for one hour
-> This bag has been carried by Mr.Lam for one hour.

d) I use this computer every day
-> This computer is used by me every day.

e) She will finish her essay in 30 minutes
-> Her essay will be finished in 30 minutes.

f) Mr.Kien said "Lan should check the bike carefully"
-> Mr.Kien suggested that Lan should check the bike carefully.

g) Hoa said "Let's come to my home"
-> Hoa suggested coming to her home.