Which was the greatest challenge for both american settlers and american indians in the west in the mid-1800s?
a. the exposure to harsh weather
b. the threat of deadly diseases
c. the danger of crossing difficult terrain
d. the problem of fenced-off land

Answer

The threat of deadly diseases

Explanation

There were endemics diseases  like malaria and dysentery  which were considered as endemics because they did not end completely after  cure but they recurred years after years.

At the time, medicine was not as advanced as it is today, so even if these people contracted a disease, however harmful it may have been, often they would die because there wasn't a suitable medicine to help them fight it.  They continued because when other peoples arrived from other nations carrying germs of the diseases they had not experienced before like measles and small pox the viruses killed many of them before they could come up with preventive measures and cure for them

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.