The correct answer is: B. pneumatophores.
Pneumatophores are specialized roots that grow upwards out of the water in mangroves and other aquatic plants. They allow the plants to take in oxygen from the air, which is necessary for respiration.
Velamen is a layer of dead cells that covers the roots of some epiphytic orchids. It helps to absorb water and nutrients from the air.
Hydathodes are small pores on the leaves of some plants that release excess water vapor.
Prop roots are roots that grow from the trunk or branches of a plant and help to support it.
Pneumatophores are the only option that are specialized for respiration. The other options are specialized for other functions.