The advantage of van Leeuwenhoek's microscopes was that a. they were simple.
c. the lenses could be moved.
b. they had two lenses.
d. the lenses were ground very precisely.

D)the lenses were ground very precisely.

Explanation:

the generally accepted parts of modern cell theory include: all known living things are made up of one or more cells. all living cells arise from pre-existing cells by division. the cell is the fundamental unit of structure and function in all living organisms.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.