Answer:
When much oil was discovered in the land of the Nigerian Igbos in 1965, they wanted to rule themselves, and a bloody coup began, starting a war over Biafra, their new country.
Explanation:
The most effective combination of the given sentences is the first one. It's easy to understand and grammatically correct.
The second one is incorrect because the sentences aren't well-connected. We shouldn't use the same conjunction too many times, and here, the conjunction <em>and </em>is repeated.
In the third option, the same issue is present. Besides that, an unnecessary <em>that </em>is used before the phrase<em> much oil,</em> making the sentence additionally difficult to comprehend.
In the fourth option, we have a comma splice - a type of punctuation error, where independent clauses are connected only by a comma. Inserting a conjunction or replacing the comma with a semicolon would correct this mistake.
This is why the first option is the correct one.
