The Government must do something about the runaway increase in prices.

Answer: Option B

Unpardonable : (of a fault or offence) too severe to be pardoned; unforgivable.
Uncontrollable : not controllable.
Unreasonable : not guided by or based on good sense.
Inflationary : characterized by or tending to cause monetary inflation.
Runaway : denoting something happening or done very quickly, easily, or uncontrollably.

Synonym of Runaway is Uncontrollable