The correct answer among the choices given is option A. Eustachian, Pharynx, Bronchi are structures that ensembles a tube. The Eustachian tube is a narrow passage from the pharynx to the middle ear. Pharynx is a passageway leading from the oral and nasal cavities to the larynx and the esophagus. Lastly, bronchi is an airway in the respiratory tract.
iron Presence of trace elements, irradiation and iron impurities give the gem amethyst its purplish color!
I would say the first three. But I'm not 100% sure. I'm truly sorry if it's wrong
A covalent bond? Not sure how much detail you want, sorry
