Answer: D. None of these will increase the half life.
Step-by-step explanation:
Half life is the amount of time taken to decay to half of its original value. The half life is related to rate constant by the following relation for a first order reaction:

As half life is independent of concentration , temperature and pressure, none of these factors would affect the half life.
Thus in the reaction,
following first order kinetics, none of the factors will increase the half life.