It should not be controversial: it would only make the research less reliable since people would have their opinions about the topic that they would want to defend. It should also not be obscure: then it's hard to check.
The best answer is that it should be multifaceted: it should include a number of aspects, not just one, so that the test can check for those aspects, not just one.
Answer:
what text are you referring to?.
The answer would be began because if a barricade fell down in the middle of a confrontation and there is something that has to do with a riot it would only make sense that a riot would happen which the answer would be began.
Argumentative essay, sure. But what about? Give me a topic.