Cells were first observed in cork by ______ in 1665.

Correct option is D

The answer is (d) Robert Hooke.
Robert Hooke was an English physicist, mathematician, astronomer, architect, and inventor. He is best known for his work on optics and microscopy. In 1665, he used a microscope to observe thin slices of cork and described the small, box-like structures he saw as "cells". This was the first time that cells had been observed in any organism.
So, the correct answer is Robert Hooke, who first observed cells in cork in 1665.