Study the following statements regarding frog.
a) Eyes are simple situated in the orbit of the skull
b) In females, ureters and oviducts open separately into the cloaca.
c) Special venous connection between kidney and lower parts of the body is hepatic portal system.
d) Sinus venosus joins left atrium.
e) Male frogs can be distinguished from the by the presence of vocal sacs and copulatory pad.
f) Medulla oblongata passes through the foramen ovale and continues into spinal cord.
How many are incorrect statements?