You want to place a piece of glass tubing into a rubber stopper after the tubing has been fire polished and cooled.

A. Lubricating the tubing with water or glycerin.

B. Using a towel or cotton gloves for protection.

C. Twisting the tubing and stopper carefully.

D. All of the above.

D. All of the above

Explanation:

We can place a piece of glass tubing into rubber stopper after the tubing has been fire polished and cooled by

Lubricating the tubing with water or glycerin.

Using a towel or cotton gloves for protection.

or by

Twisting the tubing and stopper carefully.

Hence we can say that all the above methods are equally useful for the above procedure.