The teacher asked the students to do the experiment __________ small groups.
The machine has been made easier for it __________.
No matter how bright a talker you are, there are times when it's better __________ silent.
I remembered __________ the door before I left the office, but forgot to turn off the lights.
George returned after the war, only __________ that his wife had left him.
Having finished her project, she was invited by the school __________ to the new students.