Question

Whereas a semicolon separates, a colon usually:

Answer 1

Answer:

The correct answer is A. is a mark of introduction.

Explanation:

A colon introduces an element or series of elements that illustrates or amplifies the information that preceded the colon. Therefore, in a given sentence, a colon is silently interpreted as  “as follows,” or “which is/are.”  

Bearing the stated above in mind, it could be said that from the options provided the correct answer is "option A", since a colon could be seen as a mark of introduction for a series of elements that illustrates the information that preceded it.

Answer 2

I would say C. follows a transitional expression.