The effectiveness and side-effects of a drug vary from one person to the next. One reason for this is that:

    a.    most drugs interact with the diet to produce variable effects.
    b.    most drugs are chemically unstable, resulting in unpredictable effects.
    c.    drugs will break down neurotransmitters into different component parts in different people.
    *d.    each drug tends to affect more than one kind of synapse.