Question

read this excerpt from a passage. the prosperity of europe and the united states during the second half of the nineteenth century led to the brisk growth of the ivory trade. wealthy people clamored for ivory piano keys as well as for ivory combs, billiards balls, and knife handles. they also wanted works of art carved from ivory. hunters and traders (of ivory) created a network that reached around the world. as a result of the trade in ivory, the population of african elephants, which national geographic placed at approximately 26 million in 1800, was reduced drastically in a single century. by 1900, there were just 10 million african elephants left. what was an effect of the increase in demand for ivory? those in the ivory trade increased their efforts to obtain ivory causing elephant populations to substantially decline. actors in the ivory trade understood the moral issue involved in killing elephants and took steps to cease trading it. the national geographic magazine took more interest in the story and increased its reporting on the topic. ivory products, like piano keys, ivory combs, and billiards balls decreased in price due to the high demand for ivory.

Explanation:

The passage states that due to the ivory trade (caused by increased demand for ivory products like piano keys, combs, etc.), African elephant populations declined. It mentions that in 1800 there were approximately 26 million African elephants and by 1900 only 10 million were left. There is no mention in the text about the ivory - trade actors ceasing trade due to moral issues (so the second option is wrong). The mention of National Geographic is just to provide the elephant population number in 1800, not that the magazine increased reporting (so the third option is wrong). High demand for a product typically does not lead to a decrease in price (if anything, it might lead to an increase, so the fourth option is wrong).

Answer:

Those in the ivory trade increased their efforts to obtain ivory causing elephant populations to substantially decline.