Psychologists in the 19th Century Were Keenly Interested in Consciousness

Psychologists in the 19th century were keenly interested in consciousness. Why did this interest wane during most of the 20th century?

A) Psychologists believed that most of the fundamental issues around consciousness were solved, so psychologists began to examine behavior with rigorous experimental methods.
B) Psychologists believed that the conscious experience was too subjective for scientific study.
C) There were no methods available with which to study consciousness until neurophysiology discovered how synapses work and how neurons conduct nerve impulses.
D) Computers had not yet been invented, and the data from research on consciousness were simply too voluminous and complex to work with by hand.