c. Barney tells his son, "I’m so proud of how well you prepared for your biology test."
Explanation:
Barney has used the most effective strategy in praising and motivating his son. While Cornelius uses monotonous phrase for praising his daughter but without giving reason. Abdul uses a common level of praise but not for any big achievement. Ed praises his daughter but not with enthusiasm since he avoids eye contact. Darnell praises his son but adds an encouraging words which shows his son did not do well.
