An example of an adaptation to prevent water loss in plants is

One example can be the needle shaped leaves.

In desert areas, there are not much water sources. So basically, any drop of water is precious. To help prevent water loss of plants, for example cactus has very thin leaves that are needle shaped. Or some even don't have any leaves. This can reduce the surface area of leaves and thus reduce the water evaporating to the outer environment.

Another example also shown on cactus is that they have very thick waxy cuticle. It can also prevent water from evaporating from the stem. So that's why you see the stem is very shinny.

The answer would be d. pili