Final answer:
The most important factor predisposing toddlers to infections such as otitis media and tonsillitis is their short, straight internal ear/throat structures combined with large tonsil/adenoid lymph tissue.
Step-by-step explanation:
The factor most important in predisposing toddlers to frequent infections such as otitis media, tonsillitis, and upper respiratory tract infections is d. short, straight internal ear/throat structures and large tonsil/adenoid lymph tissue.
My explanation for the question is as follows: Children have anatomical differences compared to adults, including shorter and more horizontal Eustachian tubes that link the middle ear to the nasopharynx. This anatomical characteristic, paired with large lymphoid tissues like tonsils and adenoids, makes it easier for pathogens to access and infect the middle ear and throat area. In addition, the immature immune system of toddlers doesn't clear infections as efficiently as the immune system of older children and adults.