What is the main source of entry of germs into the udder in Mastitis?

The main source of entry of germs into the udder is through the teat at the time of milking.
The endogenous route is more rare, but it is common in mastitis caused as a result of brucellosis and tuberculosis.
The clinical form is easy to diagnose due to the inflammation and hardness of the udder.
The subclinical form is diagnosed through the California Test, as is done with cows.
a) Only I and II are correct.
b) Only III and IV are correct.
c) I, II and IV are correct.
d) All statements are correct.