What was John snows original hypothesis and how did it conflict with prevailing models of Heath and disease

Explanation:Snow's hypothesis was that contaminated water was the source of the disease, but the challenge was how to prove this to others who were skeptical. ... It is now known that cholera is a waterborne disease, spread when water used for drinking or washing food has been contaminated with feces from infected individuals.

the answer is a or when it says crossing over

a

explanation:

many plants naturally reproduce this way, but it can also be induced artificially. horticulturalists have developed asexual propagation techniques that use vegetative plant parts to replicate plants. success rates and difficulty of propagation vary greatly. monocotyledons typically lack a vascular cambium and therefore are harder to propagate.