The correct choice is (b) Chemical drugs which are already found in the body
To elaborate: Soft drugs are natural endogenous substances which are already present in the body. Such as neurotransmitters (dopamine, GABA, epinephrine, norepinephrine), steroids (oxytocin, oestrogen, progesterone), insulin. The body is already programmed to metabolize them and excrete out. Thus these drugs when used are rapidly inactivated.