Answer:
Darlene.
Step-by-step explanation:
Operational thinking may be defined as the third stage of the cognitive development. The individual starts thinking logically and cannot be influenced by other.
The operational thinking develops by looking at the real situation. Darlene teacher provide them hands on project. These projects involve the logical thinking of Darlene. Geoff's teacher provide simple lectures and the homework assigned simply. He is not creative and does not make effort for this. Hence, Darlene develops the operational thinking.
Thus, the answer is Darlene.