So the officials are saying that night flights have been coming since the beginning i.e. 20 yrs ago. So people should not have bought houses here if night flights were disruptive to their sleep. But they are assuming that people bought houses in the last 20 years when they knew about the night flights. What if people had actually bought the houses more than 20 yrs ago? Airport officials have no answer for them. They are assuming that everyone who is complaining had bought his/her house less than 20 yrs ago. Hence (B) is an assumption.

Option (E) only says that people who buy houses near the airport have no choice - they just can't avoid buying near the airport - could be for whatever reasons - lower prices, higher availability etc. The point is that they knew before buying that they are compromising by taking next to the airport. They pay for what they get. After getting the house, they cannot complain of the night flights (perhaps because of which the price they paid was lower). No matter what their reason was for buying the house close to the airport, if they did, they knew that sleep will get disturbed. So now they cannot cry about the disturbance. Hence officials are not answerable to people who had no choice but had to buy near the airport. So (E) is not an assumption.

Answer: B