What determines a persons caste?

"The outstanding example of Hinduism's establishment tendencies is the
caste system. The caste system divides the Hindu people into four
major classes, Brahman, Kshatriya, Vaishya, and Shudra, and
"untouchables," or people outside of all the classes. Members of
certain castes have certain duties. Caste is determined by birth,
allowing no social advancement, career choice, or individual freedom."

"Hinduism and buddhism: a comparison" PageWise, Inc. (2002)
http://sc.essortment.com/hinduismandbud_rtqs.htm

Search terms: caste system determination

Sincerely,

Wonko

I want to correct the answer.

Shudra is same as "untouchables," and there is no such thing in
Hinduism as "people outside of all the classes".

Not all Shudras are "untouchables", they have sub-castes too, in fact
most of the Shudra are not "untouchables". Farmers, blacksmith etc
Shudra but can be touched by Brahmins.