Solution:Sentence B will be the starting line as it contains the main idea of the parajumble i.e. observation made by Spanish scientist Santiago Ramón y Cajal.
However, Sentence A states that according to his hypothesis, each nerve cell communicates with others through contiguity rather than continuity.
So, A will follow B. Further, Sentence D states that communication between adjacent but separate cells must take place across the space and barriers separating them & Sentence C states that it has since been proved that Cajal's theory is not universally true, but his central idea has remained an accurate guiding principle for all further study.
So, C will follow D. Going through the options, option c has the correct sequence.