Final answer:
In Christian theology, it is believed that through Adam, sin entered into the world, which is a core reason for the need for redemption and salvation in this belief system. The correct option in reference to what entered the world through Adam is: a) Sin.
Step-by-step explanation:
St. Paul wrote that "by one man sin entered into the world," referring to the Biblical figure Adam. This is grounded in Christian theology which states that through Adam's disobedience in the Garden of Eden, sin was introduced to humanity. This concept is central to Christian beliefs about the need for redemption and salvation, which is fulfilled through the sacrifice of Jesus Christ, often referred to as the second Adam. In contrast to the fall of Adam and Eve which brought sin and expulsion from paradise, Mary and Christ are seen as offering a path to eternal life for humanity through Christ’s sacrifice on the cross. The correct option in reference to what entered the world through Adam is: a) Sin. This is tied to original sin and sets up foundational theological concepts that would influence many aspects of Christianity, including the notions of atonement and redemption.