Final answer:
ABA has been shown to be effective for treating depression and smoking, but not for modifying motivation to engage in a behavior.
Step-by-step explanation:
ABA, which stands for Applied Behavior Analysis, has been shown to be effective for treating depression and smoking. For example, ABA techniques such as cognitive-behavioral therapy (CBT) have been used successfully to treat depression by identifying and modifying negative thought patterns and behaviors.
However, ABA has NOT been shown to be effective for treating some conditions or behaviors, such as motivation to engage in a specific behavior. In animal research, it has been found that ABA is effective in modifying the behavior of male rats in the nucleus accumbens, but not the motivation to engage in that behavior.
Therefore, the correct answer is option C: neither a nor b, as ABA has been shown to be effective for treating depression and smoking, but not for modifying the motivation to engage in a behavior.