Answer
D. transparent.
Explanation.
Materials can be classified into three in relation to how light pass through them.
Translucent. These are materials that allow light to pass through them but you can not see through them. A good example of this material is the glass that is used to make doors of a bathroom.
Opaque. These are material that cannot at all allow light to go through them. Examples are; Thick metals, concrete, wood and many others.
Transparent. Theses are materials that allow light to go through them and also you can see through them. A good example is the windscreen of a car.
With this information the correct answer is D. transparent.