Circle the letter of the phrase that best completes the sentence.
The cell theory was
a. first identified in 1665
b. the end result of many scientific investigations.
c. described by Rudolf Virchow.
d. Both (a) and (b)
Explanation: the cell theory took many years to fully learn about and publish and many different scientists, biologists etc had to investigate in order to finalise the hypothesis. Also, it was first identified in 1665 by Robert hooke.
