Final answer:
Wilhelm Wundt emphasized the use of measurement and systematic observation in his studies of various aspects of psychology. The answer is option D.
Step-by-step explanation:
As Wilhelm Wundt studied vision, hearing, taste, touch, memory, and time perception, he insisted on the use of measurement and systematic observation. Wundt is known as the first person to be referred to as a psychologist and is famous for his work in establishing psychology as a distinct scientific discipline. He emphasized a methodical approach to understanding the components of consciousness and their combination to result in our conscious experience.
Wundt's techniques involved experimental introspection which was an objective examination of one's own conscious experience, paralleling the scientific observation methods applied to natural phenomena. Therefore, the correct answer to the student's question is 'systematic observation'.