The correct option is A Cyclobutane
Parent chain = cyclobutane (four-carbon ring)
Numbers start from the carbon with the butyl substituent and go counter-clockwise. Starting from the butyl(counter-clockwise) or chloro(clockwise) would give the same numbering (1,2,3). So, butyl is chosen over chloro as carbon 1 because it is first alphabetically.
Substituents=1−butyl2−bromo3−chloro