Most UFO sightings occur at (a)(at, in, on) night, either late in the evening or in the early hours of the morning. (b)(as, while, often) As they take place on a dark moonless night when the person (c)(are, is, were) is alone on a country road. This eerie atmosphere is perfect (d)(for, off, on) a person's imagination. Police and newspaper officers are often swamped (c)(with, among, for) calls when something strange is seen in the skies. (f)(once, before, when) an explanation is given, most people are happy to accept it.