—How long have you been in Qiqihar?
—________ my father came here to work five years ago.
When
While
Since
Turn off the water while you ________ your teeth or washing your hands.
It ________ about eight minutes for sunlight (阳光) to travel from the sun to the earth.
Talk to your teacher and you will get help ________ you have a problem.
We have friends to help us fight against pollution, and trees are one of ________.
Now, people regard drinking tea ________ a culture more than a habit.