Question

although attaining a height of fifteen to sixteen feet, the trachodons were not covered with scales or a bony protecting ______, but with dermal tubercles of relatively small size.
source: dinosaurs with special reference to the american museum collections
armature
capillary
tentacle
esophagus

Explanation:

The context indicates a protective - like structure for the trachodons. "Armature" means a defensive covering or structure, which fits the context as it contrasts with scales or bony protection. "Capillary" is related to tiny blood vessels, "tentacle" is a flexible limb - like organ, and "esophagus" is a part of the digestive system, none of which fit the context of protective covering.

Answer:

A. armature