Mechanism of Breathing

Inspiration is initiated by the contraction of the diaphragm, which increases the volume of the thoracic chamber in the antero-posterior axis. Contraction of the external intercostal muscles increases the volume in the dorso-ventral axis. This increases pulmonary volume and decreases intra-pulmonary pressure, so air flows in. So (a) and (b) are correct.

Breathing is brought about by the diaphragm and the intercostal muscles; contraction of the diaphragm increases the thoracic volume in the antero-posterior axis, and the ribs change it in the dorso-ventral axis.
With conscious effort one can breathe in and out using the diaphragm alone (abdominal breathing) without moving the ribs.
The lungs can never be emptied completely: even after the most forceful expiration about 1100–1200 mL of air (residual volume) remains.
Expired air always contains oxygen (about 16%), so it cannot be made totally free of oxygen.
The Eustachian tubes connect the middle ear to the pharynx and end at the closed ear drum, so air cannot be breathed out through them.
Hence the possibility is breathing by moving the diaphragm alone.