The intermolecular force(s) responsible for the fact that CH₄ has the lowest boiling point in the set CH₄, CH₃CH₃, CH₃CH₂CH₃, CH₃CH₂CH₂CH₃ is/are

A) hydrogen bonding
B) dispersion forces
C) mainly hydrogen bonding but also dipole forces D) dipole forces
E) mainly dispersion forces but also dipole forces