Correct Option: D

weak (Adjective) : not physically strong ; likely to break ; not having much power
potent (Adjective) : having a strong effect on your mind/ body; powerful
inefficient (Adjective) : not doing a job well and not making the best use of time, money, energy, etc.
soft (Adjective) : very brittle
fragile (Adjective) : easily broken/damaged ; weak and uncertain