Chuyển câu bị động ở thì quá khứ đơn : 1, Nobody swept this street last week.     => 2, they looked after the chidren caerfully.   => 3, Where did they buy that skirt ?     => 4, Mr.Obama had " Bún chả " at Huong Lien food stall .    => 5, They did not decorate the room yesterday.    =>