Read the passage about genetic erosion in black rhinoceros populations, and then answer: from the second half of the twentieth century, what factor has caused a dramatic fall in black rhinoceros population and genetic diversity?

Introduction / Context:
This question again draws on the reading passage about black rhinoceros in sub Saharan Africa, but now focuses on identifying the main cause for the dramatic fall in population from the second half of the twentieth century. The passage distinguishes between earlier historical influences, such as colonial rule and big game hunting, and more recent pressures. Understanding this timeline and the specific wording used by the author is essential for choosing the correct answer.

Given Data / Assumptions:
• The passage says that the origins of genetic erosion coincided with colonial rule in Africa and the popularity of big game hunting. • It then states that from the second half of the twentieth century, poaching for horns has dramatically depleted black rhinoceros population and genetic diversity. • The question asks specifically about the second half of the twentieth century. • Several options echo phrases from the passage, but they refer to different time periods or concepts.

Concept / Approach:
The key reading strategy here is to pay attention to time markers. The phrase "from the second half of the twentieth century" narrows the relevant part of the passage. You must then identify what the author mentions as happening in that time frame. Although colonial rule and big game hunting are linked to the beginnings of genetic erosion, the dramatic depletion in more recent decades is specifically connected to poaching for horns. Recognising and respecting these chronological distinctions is a common theme in reading comprehension questions about history and science.

Step-by-Step Solution:
1. Re read the part of the passage that mentions the second half of the twentieth century. 2. Note the exact wording: from that period onward, poaching for horns has dramatically depleted population and genetic diversity. 3. Contrast this with the earlier line that links genetic erosion to colonial rule and big game hunting. 4. Understand that colonial rule and big game hunting are historical roots of the problem but are not described as the main recent cause. 5. Compare each option with these observations. 6. Identify "Poaching for horns" as the only option that exactly matches the factor named for the second half of the twentieth century.

Verification / Alternative check:
One useful check is to ask what specific activity continues to be a threat to black rhinoceros in modern times. Conservation reports and general knowledge also confirm that illegal hunting for horns is one of the biggest dangers for rhinos. This outside understanding agrees with what the passage states. When you align this with the text that says poaching for horns has dramatically depleted population and genetic diversity, it confirms that option A is correct and that the other options describe older or less precise influences.

Why Other Options Are Wrong:
Option B, colonial rule in Africa, is mentioned as part of the historical context that coincided with the beginning of genetic erosion, but it is not given as the main recent cause for dramatic loss from the second half of the twentieth century. Option C, big game hunting, again belongs to an earlier period and is not the key modern factor specified in the passage. Option D, a natural fall in genetic diversity, misrepresents the text, because the passage emphasises human pressures rather than natural processes as the main cause. None of these options captures the time specific activity identified in the question.

Common Pitfalls:
A common trap is to pick a phrase that appears early in the passage without taking careful note of time markers. Students might remember "colonial rule" and "big game hunting" more easily because they appear in a prominent sentence but forget that the question asks about the second half of the twentieth century. Another error is to assume that genetic diversity falls naturally over time, whereas the passage points to human actions. Always match the question words, such as time expressions, with the relevant part of the text before selecting an answer.

Final Answer:
From the second half of the twentieth century onward, the dramatic fall in black rhinoceros population has been caused mainly by poaching for horns.