41.   The other tube will be open to traffic in both directions at the same time.

42.   The other tube will be open to traffic in each direction.

43.   The signs are a reminder that the tube is off-limits for an entire week.

44.   The telltale mud tubes are very distinctive.

45.   The tube is fraught with them.

46.   The tubes are essentially rolled-up sheets of graphite, one of the basic forms of carbon.

47.   The tubes may be stacked in any order your child pleases.

48.   The tube is then snaked up a major artery to the affected area.

49.   The tubes are visible, though they are behind a cage.

50.   The suction tube is Mr. Thirsty, and the rubber-tipped drill is the tickle brush.