Which of the following best describes the microscopic structure of the liver?
a. Hexagonal plates of hepatocytes surrounding a central vein with portal triads at each corner
b. Octagonal plates of hepatocytes surrounding a central artery with portal triads at each corner
c. Irregular groups of hepatocytes surrounding a central vein with bile ducts at each corner
d. Hexagonal plates of hepatocytes surrounding a portal vein with bile ducts at each corner