The argument concludes that compared to reading newspapers, watching TV news makes viewers more likely to hold oversimplified views about public issues. This is supported by a whole lot of information about both TV news and newspapers, which we can divide into two causal chains.

Discussing TV news, the argument says that in general, those advocating for a point of view only get 30 seconds to make their point. This causes regular viewers to habitually think about issues in terms of slogans and catchphrases. In turn, this habit causes these regular viewers not to expect a careful discussion of public issues.

Discussing newspapers, the argument says that newspaper stories encourages readers to "pursue details of stories headed by the most important facts." This causes newspaper readers to expect a careful discussion of public issues. The comparison with TV news then supports the argument's conclusion.

Because this is a reasonably complex causal argument, it's difficult to identify any one necessary assumption to hunt for. There are assumptions built in at every point of the two causal chains, in the jump from "expecting careful discussion" to "oversimplified views" in the conclusion, and so on. So our best strategy will be process of elimination.

Incorrect answer choices will be unnecessary to the argument. They might be related—they might even strengthen—but they won't be essential for the argument to make sense. We can check this using the "must be true" and "negation" tests. If an answer choice must be true for the argument to make sense, it's necessary. Conversely, if we can negate an answer choice without the argument falling apart, it's not necessary.