Materials for rain-proof coats and tents owe their water-proof properties to A. surface tension B. viscosity C. specific gravity D. elasticity

The correct answer is: A. surface tension.

Surface tension is a property of water that allows it to form a thin film on top of other surfaces. This film is what makes water droplets bead up on a surface, and it is also what allows rain-proof coats and tents to keep water out.

B. Viscosity is a measure of how thick or thin a liquid is. It has nothing to do with water-proofing.

C. Specific gravity is a measure of how dense a substance is compared to water. It has nothing to do with water-proofing.

D. Elasticity is a measure of how much a substance can stretch before it breaks. It has nothing to do with water-proofing.