Question

select the independent clause.
at the veterans day parade, i proudly shook hands with a lieutenant colonel who
had served in the marines during the vietnam war.

Explanation:

An independent clause has a subject and a predicate and can stand alone as a sentence. In the given sentence, "I proudly shook hands with a lieutenant colonel" has the subject "I" and the predicate "proudly shook hands with a lieutenant colonel" and can function as a complete sentence. The other parts ("At the Veterans Day parade" is a prepositional phrase, "who had served in the marines during the Vietnam War" is a dependent (relative) clause) are not independent.

Answer:

I proudly shook hands with a lieutenant colonel