(2013·北京，21)Volunteering gives you a chance ________ lives, including your own.
A．change B．changing C．changed D．to change
________ several times，but he still doesn't know how to do it correctly.
A．Although I've taught him
B．I've taught him
C．Having been taught
D．Having taught
Information technology is taught in most schools，________ we have entered the information era.
A．so B．while
C．for D．still
It's really very dangerous.One more step，________ the baby will fall into the well.
A．or B．so C．but D．and
There is still much to discuss；________，we shall return to this topic at the next meeting.
A．yet B．therefore
C．otherwise D．however
Knowledge is the food of thought ________，as long as it is put in our brain，we will grow wiser.
A．but B．when C．then D．and
