Supply the appropriate word/words to complete the following passages:
Most UFO sightings occur (a) ............. the night, either late in the evening or in the early hours of the morning. (b) ............. they take place on a dark moonless night when the person (c) ............. alone on a country road. This eerie atmosphere is perfect (d) ............. playing tricks on a person’s imagination. Police and newspaper officers are often swamped (e) ............. calls when something strange is seen in the skies. Once, (f ) ............. is given, most people are happy to accept it. But they are always keen to know why (g) ............. things happen and what (h) ............. the cause for such happenings.