Final answer:
The tubing becomes thinner and the cross-sectional area decreases when it is stretched, due to the conservation of volume and the properties of materials under tension.
Correct option is C
Step-by-step explanation:
When a piece of rubber tubing is stretched, the correct statement about the shape of the tubing is that the tubing becomes thinner, causing the cross-sectional area to decrease. This effect is due to the conservation of volume; as the length of an object increases, the cross-section must decrease for the volume to remain constant. This is known as Poisson's effect, which is often observed in the stretching of materials.
Assuming the volume of the rubber tubing stays the same during the stretching process, the shape of the tubing changes as it elongates. As depicted in Figure 12.3, which refers to the fluid dynamics in a tube, the principle can analogously apply to the material of the tubing when subjected to tensile stress, leading to a smaller cross-sectional area and longer length.