Which is correct? select one of the options below as your
a. joe isn't allowed to leave work on saturday, until his replacement shows up.
b. joe isn't allowed to leave work on saturday until his replacement shows up.

In a sentence, a comma is inserted to represent a separation of the elements in a list or as a marker for the representation of a new thought. In the sentence "Joe isn't allowed to leave work on Saturday [,] until his replacement shows up.", there is one complete thought running through the entire sentence, and therefore no grammatically correct reason to insert a comma.
Your correct answer choice is B: "Joe isn't allowed to leave work on Saturday until his replacement shows up."
Hope that helped! =)

D. a subtle indirect reference

Explanation:

An allusion is a reference, from a literary work to another work of fiction, a film, a piece of art, or even a real event. An allusion can be used as a straightforward device to enhance a text by providing further meaning, but it can also be used in a more complex sense to make an ironic comment on one thing by comparing it to something that is dissimilar. It's an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.