Which is the closest relative in your direct line who was an Argentine citizen?
Argentina — Citizenship by Descent
Your direct line means you, your parents, their parents, and so on back — not aunts, uncles or cousins, and not a spouse's family. If you were born in Argentina yourself, say so: that answers the question on its own. If more than one line goes back to Argentina, pick the closest one; the others can be looked at separately.