Hint: Ascent of sap is a phenomenon that takes place in the xylem tissue and can be described as the upward movement of water and minerals that are absorbed from the root and reaches to the crown of the plant.
Scientist Strasburger is a German Botanist who was the first person in the field of Biology to describe the embryonic sac theory in gymnosperms and angiosperms.
Richard Newland Dixon is a well known British Chemist who was the first person to describe the optical or thermal properties of matter.
Katherine Esau was a German-American Botanist. She contributed a lot in the field of plant anatomy.
The best vital theory was proposed by Scientist Godlewski.
The theory was proposed to elaborate the concept of ascent of sap in plants.
So, the correct answer is option A. Godlewski.
Note: There were two vital force theories – Relay pump theory and Rhythmic pulsation theory.
The first one is proposed by Dr. Godlewski and the later one is proposed by Dr. J. C. Bosse.