One Meta-Analysis (Griffith Et Al

One meta-analysis (Griffith et al.,2000) of the effectiveness of contingency management in reducing drug use showed that:

A) smaller but more frequent reinforcers led to better treatment results.
B) medium sized and delayed reinforcers led to better treatment results.
C) larger and more immediate reinforcers led to better treatment results.
D) the size and interval of reinforcers had no impact on treatment results.